[go: nahoru, domu]
  1. 15 Rendering
    1. 15.1 Introduction
    2. 15.2 The CSS user agent style sheet and presentational hints
    3. 15.3 Non-replaced elements
      1. 15.3.1 Hidden elements
      2. 15.3.2 The page
      3. 15.3.3 Flow content
      4. 15.3.4 Phrasing content
      5. 15.3.5 Bidirectional text
      6. 15.3.6 Sections and headings
      7. 15.3.7 Lists
      8. 15.3.8 Tables
      9. 15.3.9 Margin collapsing quirks
      10. 15.3.10 Form controls
      11. 15.3.11 The hr element
      12. 15.3.12 The fieldset and legend elements
    4. 15.4 Replaced elements
      1. 15.4.1 Embedded content
      2. 15.4.2 Images
      3. 15.4.3 Attributes for embedded content and images
      4. 15.4.4 Image maps
    5. 15.5 Widgets
      1. 15.5.1 Native appearance
      2. 15.5.2 Writing mode
      3. 15.5.3 Button layout
      4. 15.5.4 The button element
      5. 15.5.5 The details and summary elements
      6. 15.5.6 The input element as a text entry widget
      7. 15.5.7 The input element as domain-specific widgets
      8. 15.5.8 The input element as a range control
      9. 15.5.9 The input element as a color well
      10. 15.5.10 The input element as a checkbox and radio button widgets
      11. 15.5.11 The input element as a file upload control
      12. 15.5.12 The input element as a button
      13. 15.5.13 The marquee element
      14. 15.5.14 The meter element
      15. 15.5.15 The progress element
      16. 15.5.16 The select element
      17. 15.5.17 The textarea element
    6. 15.6 Frames and framesets
    7. 15.7 Interactive media
      1. 15.7.1 Links, forms, and navigation
      2. 15.7.2 The title attribute
      3. 15.7.3 Editing hosts
      4. 15.7.4 Text rendered in native user interfaces
    8. 15.8 Print media
    9. 15.9 Unstyled XML documents

15 Rendering

User agents are not required to present HTML documents in any particular way. However, this section provides a set of suggestions for rendering HTML documents that, if followed, are likely to lead to a user experience that closely resembles the experience intended by the documents' authors. So as to avoid confusion regarding the normativity of this section, "must" has not been used. Instead, the term "expected" is used to indicate behavior that will lead to this experience. For the purposes of conformance for user agents designated as supporting the suggested default rendering, the term "expected" in this section has the same conformance implications as "must".

15.1 Introduction

The suggestions in this section are generally expressed in CSS terms. User agents are expected to either support CSS, or translate from the CSS rules given in this section to approximations for other presentation mechanisms.

In the absence of style-layer rules to the contrary (e.g. author style sheets), user agents are expected to render an element so that it conveys to the user the meaning that the element represents, as described by this specification.

The suggestions in this section generally assume a visual output medium with a resolution of 96dpi or greater, but HTML is intended to apply to multiple media (it is a media-independent language). User agent implementers are encouraged to adapt the suggestions in this section to their target media.

An element is being rendered if it has any associated CSS layout boxes, SVG layout boxes, or some equivalent in other styling languages.

Just being off-screen does not mean the element is not being rendered. The presence of the hidden attribute normally means the element is not being rendered, though this might be overridden by the style sheets.

The fully active state does not affect whether an element is being rendered or not. Even if a document is not fully active and not shown at all to the user, elements within it can still qualify as "being rendered".

An element is said to intersect the viewport when it is being rendered and its associated CSS layout box intersects the viewport.

Similar to the being rendered state, elements in non-fully active documents can still intersect the viewport. The viewport is not shared between documents and might not always be shown to the user, so an element in a non-fully active document can still intersect the viewport associated with its document.

This specification does not define the precise timing for when the intersection is tested, but it is suggested that the timing match that of the Intersection Observer API. [INTERSECTIONOBSERVER]

An element is delegating its rendering to its children if it is not being rendered but its children (if any) could be rendered, as a result of CSS 'display: contents', or some equivalent in other styling languages. [CSSDISPLAY]

User agents that do not honor author-level CSS style sheets are nonetheless expected to act as if they applied the CSS rules given in these sections in a manner consistent with this specification and the relevant CSS and Unicode specifications. [CSS] [UNICODE] [BIDI]

This is especially important for issues relating to the 'display', 'unicode-bidi', and 'direction' properties.

15.2 The CSS user agent style sheet and presentational hints

The CSS rules given in these subsections are, except where otherwise specified, expected to be used as part of the user-agent level style sheet defaults for all documents that contain HTML elements.

Some rules are intended for the author-level zero-specificity presentational hints part of the CSS cascade; these are explicitly called out as presentational hints.

When the text below says that an attribute attribute on an element element maps to the pixel length property (or properties) properties, it means that if element has an attribute attribute set, and parsing that attribute's value using the rules for parsing non-negative integers doesn't generate an error, then the user agent is expected to use the parsed value as a pixel length for a presentational hint for properties.

When the text below says that an attribute attribute on an element element maps to the dimension property (or properties) properties, it means that if element has an attribute attribute set, and parsing that attribute's value using the rules for parsing dimension values doesn't generate an error, then the user agent is expected to use the parsed dimension as the value for a presentational hint for properties, with the value given as a pixel length if the dimension was a length, and with the value given as a percentage if the dimension was a percentage.

When the text below says that an attribute attribute on an element element maps to the dimension property (ignoring zero) (or properties) properties, it means that if element has an attribute attribute set, and parsing that attribute's value using the rules for parsing nonzero dimension values doesn't generate an error, then the user agent is expected to use the parsed dimension as the value for a presentational hint for properties, with the value given as a pixel length if the dimension was a length, and with the value given as a percentage if the dimension was a percentage.

When the text below says that a pair of attributes w and h on an element element map to the aspect-ratio property, it means that if element has both attributes w and h, and parsing those attributes' values using the rules for parsing non-negative integers doesn't generate an error for either, then the user agent is expected to use the parsed integers as a presentational hint for the 'aspect-ratio' property of the form auto w / h.

When the text below says that a pair of attributes w and h on an element element map to the aspect-ratio property (using dimension rules), it means that if element has both attributes w and h, and parsing those attributes' values using the rules for parsing dimension values doesn't generate an error or return a percentage for either, then the user agent is expected to use the parsed dimensions as a presentational hint for the 'aspect-ratio' property of the form auto w / h.

When a user agent is to align descendants of a node, the user agent is expected to align only those descendants that have both their 'margin-inline-start' and 'margin-inline-end' properties computing to a value other than 'auto', that are over-constrained and that have one of those two margins with a used value forced to a greater value, and that do not themselves have an applicable align attribute. When multiple elements are to align a particular descendant, the most deeply nested such element is expected to override the others. Aligned elements are expected to be aligned by having the used values of their margins on the line-left and line-right sides be set accordingly. [CSSLOGICAL] [CSSWM]

15.3 Non-replaced elements

15.3.1 Hidden elements

@namespace "http://www.w3.org/1999/xhtml";

area, base, basefont, datalist, head, link, meta, noembed,
noframes, param, rp, script, style, template, title {
  display: none;
}

[hidden]:not([hidden=until-found i]):not(embed) {
  display: none;
}

[hidden=until-found i]:not(embed) {
  content-visibility: hidden;
}

embed[hidden] { display: inline; height: 0; width: 0; } 

input[type=hidden i] { display: none !important; }

@media (scripting) {
  noscript { display: none !important; }
}

15.3.2 The page

@namespace "http://www.w3.org/1999/xhtml";

html, body { display: block; }

For each property in the table below, given a body element, the first attribute that exists maps to the pixel length property on the body element. If none of the attributes for a property are found, or if the value of the attribute that was found cannot be parsed successfully, then a default value of 8px is expected to be used for that property instead.

Property Source
'margin-top' The body element's marginheight attribute
The body element's topmargin attribute
The body element's container frame element's marginheight attribute
'margin-right' The body element's marginwidth attribute
The body element's rightmargin attribute
The body element's container frame element's marginwidth attribute
'margin-bottom' The body element's marginheight attribute
The body element's bottommargin attribute
The body element's container frame element's marginheight attribute
'margin-left' The body element's marginwidth attribute
The body element's leftmargin attribute
The body element's container frame element's marginwidth attribute

If the body element's node document's node navigable is a child navigable, and the container of that navigable is a frame or iframe element, then the container frame element of the body element is that frame or iframe element. Otherwise, there is no container frame element.

The above requirements imply that a page can change the margins of another page (including one from another origin) using, for example, an iframe. This is potentially a security risk, as it might in some cases allow an attack to contrive a situation in which a page is rendered not as the author intended, possibly for the purposes of phishing or otherwise misleading the user.

If a Document's node navigable is a child navigable, then it is expected to be positioned and sized to fit inside the content box of the container of that navigable. If the container is not being rendered, the navigable is expected to have a viewport with zero width and zero height.

If a Document's node navigable is a child navigable, the container of that navigable is a frame or iframe element, that element has a scrolling attribute, and that attribute's value is an ASCII case-insensitive match for the string "off", "noscroll", or "no", then the user agent is expected to prevent any scrollbars from being shown for the viewport of the Document's node navigable, regardless of the 'overflow' property that applies to that viewport.

When a body element has a background attribute set to a non-empty value, the new value is expected to be encoding-parsed-and-serialized relative to the element's node document, and if that does not return failure, the user agent is expected to treat the attribute as a presentational hint setting the element's 'background-image' property to the return value.

When a body element has a bgcolor attribute set, the new value is expected to be parsed using the rules for parsing a legacy color value, and if that does not return failure, the user agent is expected to treat the attribute as a presentational hint setting the element's 'background-color' property to the resulting color.

When a body element has a text attribute, its value is expected to be parsed using the rules for parsing a legacy color value, and if that does not return failure, the user agent is expected to treat the attribute as a presentational hint setting the element's 'color' property to the resulting color.

When a body element has a link attribute, its value is expected to be parsed using the rules for parsing a legacy color value, and if that does not return failure, the user agent is expected to treat the attribute as a presentational hint setting the 'color' property of any element in the Document matching the :link pseudo-class to the resulting color.

When a body element has a vlink attribute, its value is expected to be parsed using the rules for parsing a legacy color value, and if that does not return failure, the user agent is expected to treat the attribute as a presentational hint setting the 'color' property of any element in the Document matching the :visited pseudo-class to the resulting color.

When a body element has an alink attribute, its value is expected to be parsed using the rules for parsing a legacy color value, and if that does not return failure, the user agent is expected to treat the attribute as a presentational hint setting the 'color' property of any element in the Document matching the :active pseudo-class and either the :link pseudo-class or the :visited pseudo-class to the resulting color.

15.3.3 Flow content

@namespace "http://www.w3.org/1999/xhtml";

address, blockquote, center, dialog, div, figure, figcaption, footer, form,
header, hr, legend, listing, main, p, plaintext, pre, search, xmp {
  display: block;
}

blockquote, figure, listing, p, plaintext, pre, xmp {
  margin-block: 1em;
}

blockquote, figure { margin-inline: 40px; }

address { font-style: italic; }
listing, plaintext, pre, xmp {
  font-family: monospace; white-space: pre;
}

dialog:not([open]) { display: none; }
dialog {
  position: absolute;
  inset-inline-start: 0; inset-inline-end: 0;
  width: fit-content;
  height: fit-content;
  margin: auto;
  border: solid;
  padding: 1em;
  background-color: Canvas;
  color: CanvasText;
}
dialog:modal {
  position: fixed;
  overflow: auto;
  inset-block: 0;
  max-width: calc(100% - 6px - 2em);
  max-height: calc(100% - 6px - 2em);
}
dialog::backdrop {
  background: rgba(0,0,0,0.1);
}

[popover]:not(:popover-open):not(dialog[open]) {
  display:none;
}

dialog:popover-open {
  display:block;
}

[popover] {
  position: fixed;
  inset: 0;
  width: fit-content;
  height: fit-content;
  margin: auto;
  border: solid;
  padding: 0.25em;
  overflow: auto;
  color: CanvasText;
  background-color: Canvas;
}

:popover-open::backdrop {
  position: fixed;
  inset: 0;
  pointer-events: none !important;
  background-color: transparent;
}

slot {
  display: contents;
}

The following rules are also expected to apply, as presentational hints:

@namespace "http://www.w3.org/1999/xhtml";

pre[wrap] { white-space: pre-wrap; }

In quirks mode, the following rules are also expected to apply:

@namespace "http://www.w3.org/1999/xhtml";

form { margin-block-end: 1em; }

The center element, and the div element when it has an align attribute whose value is an ASCII case-insensitive match for either the string "center" or the string "middle", are expected to center text within themselves, as if they had their 'text-align' property set to 'center' in a presentational hint, and to align descendants to the center.

The div element, when it has an align attribute whose value is an ASCII case-insensitive match for the string "left", is expected to left-align text within itself, as if it had its 'text-align' property set to 'left' in a presentational hint, and to align descendants to the left.

The div element, when it has an align attribute whose value is an ASCII case-insensitive match for the string "right", is expected to right-align text within itself, as if it had its 'text-align' property set to 'right' in a presentational hint, and to align descendants to the right.

The div element, when it has an align attribute whose value is an ASCII case-insensitive match for the string "justify", is expected to full-justify text within itself, as if it had its 'text-align' property set to 'justify' in a presentational hint, and to align descendants to the left.

15.3.4 Phrasing content

@namespace "http://www.w3.org/1999/xhtml";

cite, dfn, em, i, var { font-style: italic; }
b, strong { font-weight: bolder; }
code, kbd, samp, tt { font-family: monospace; }
big { font-size: larger; }
small { font-size: smaller; }

sub { vertical-align: sub; }
sup { vertical-align: super; }
sub, sup { line-height: normal; font-size: smaller; }

ruby { display: ruby; }
rt { display: ruby-text; }

:link { color: #0000EE; }
:visited { color: #551A8B; }
:link:active, :visited:active { color: #FF0000; }
:link, :visited { text-decoration: underline; cursor: pointer; }

:focus-visible { outline: auto; }

mark { background: yellow; color: black; } /* this color is just a suggestion and can be changed based on implementation feedback */

abbr[title], acronym[title] { text-decoration: dotted underline; }
ins, u { text-decoration: underline; }
del, s, strike { text-decoration: line-through; }

q::before { content: open-quote; }
q::after { content: close-quote; }

br { display-outside: newline; } /* this also has bidi implications */
nobr { white-space: nowrap; }
wbr { display-outside: break-opportunity; } /* this also has bidi implications */
nobr wbr { white-space: normal; }

The following rules are also expected to apply, as presentational hints:

@namespace "http://www.w3.org/1999/xhtml";

br[clear=left i] { clear: left; }
br[clear=right i] { clear: right; }
br[clear=all i], br[clear=both i] { clear: both; }

For the purposes of the CSS ruby model, runs of children of ruby elements that are not rt or rp elements are expected to be wrapped in anonymous boxes whose 'display' property has the value 'ruby-base'. [CSSRUBY]

When a particular part of a ruby has more than one annotation, the annotations should be distributed on both sides of the base text so as to minimize the stacking of ruby annotations on one side.

When it becomes possible to do so, the preceding requirement will be updated to be expressed in terms of CSS ruby. (Currently, CSS ruby does not handle nested ruby elements or multiple sequential rt elements, which is how this semantic is expressed.)

User agents that do not support correct ruby rendering are expected to render parentheses around the text of rt elements in the absence of rp elements.

User agents are expected to support the 'clear' property on inline elements (in order to render br elements with clear attributes) in the manner described in the non-normative note to this effect in CSS.

The initial value for the 'color' property is expected to be black. The initial value for the 'background-color' property is expected to be 'transparent'. The canvas's background is expected to be white.

When a font element has a color attribute, its value is expected to be parsed using the rules for parsing a legacy color value, and if that does not return failure, the user agent is expected to treat the attribute as a presentational hint setting the element's 'color' property to the resulting color.

When a font element has a face attribute, the user agent is expected to treat the attribute as a presentational hint setting the element's 'font-family' property to the attribute's value.

When a font element has a size attribute, the user agent is expected to use the following steps, known as the rules for parsing a legacy font size, to treat the attribute as a presentational hint setting the element's 'font-size' property:

  1. Let input be the attribute's value.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Skip ASCII whitespace within input given position.

  4. If position is past the end of input, there is no presentational hint. Return.

  5. If the character at position is a U+002B PLUS SIGN character (+), then let mode be relative-plus, and advance position to the next character. Otherwise, if the character at position is a U+002D HYPHEN-MINUS character (-), then let mode be relative-minus, and advance position to the next character. Otherwise, let mode be absolute.

  6. Collect a sequence of code points that are ASCII digits from input given position, and let the resulting sequence be digits.

  7. If digits is the empty string, there is no presentational hint. Return.

  8. Interpret digits as a base-ten integer. Let value be the resulting number.

  9. If mode is relative-plus, then increment value by 3. If mode is relative-minus, then let value be the result of subtracting value from 3.

  10. If value is greater than 7, let it be 7.

  11. If value is less than 1, let it be 1.

  12. Set 'font-size' to the keyword corresponding to the value of value according to the following table:

    value 'font-size' keyword
    1 'x-small'
    2 'small'
    3 'medium'
    4 'large'
    5 'x-large'
    6 'xx-large'
    7 'xxx-large'

15.3.5 Bidirectional text

@namespace "http://www.w3.org/1999/xhtml";

[dir]:dir(ltr), bdi:dir(ltr), input[type=tel i]:dir(ltr) { direction: ltr; }
[dir]:dir(rtl), bdi:dir(rtl) { direction: rtl; }

address, blockquote, center, div, figure, figcaption, footer, form, header, hr,
legend, listing, main, p, plaintext, pre, summary, xmp, article, aside, h1, h2,
h3, h4, h5, h6, hgroup, nav, section, search, table, caption, colgroup, col,
thead, tbody, tfoot, tr, td, th, dir, dd, dl, dt, menu, ol, ul, li, bdi, output,
[dir=ltr i], [dir=rtl i], [dir=auto i] {
  unicode-bidi: isolate; 
}

bdo, bdo[dir] { unicode-bidi: isolate-override; } 

input[dir=auto i]:is([type=search i], [type=tel i], [type=url i],
[type=email i]), textarea[dir=auto i], pre[dir=auto i] {
  unicode-bidi: plaintext;
}
/* see prose for input elements whose type attribute is in the Text state */

/* the rules setting the 'content' property on br and wbr elements also has bidi implications */

When an input element's dir attribute is in the auto state and its type attribute is in the Text state, then the user agent is expected to act as if it had a user-agent-level style sheet rule setting the 'unicode-bidi' property to 'plaintext'.

Input fields (i.e. textarea elements, and input elements when their type attribute is in the Text, Search, Telephone, URL, or Email state) are expected to present an editing user interface with a directionality that matches the element's 'direction' property.

When the document's character encoding is ISO-8859-8, the following rules are additionally expected to apply, following those above: [ENCODING]

@namespace "http://www.w3.org/1999/xhtml";

address, blockquote, center, div, figure, figcaption, footer, form, header, hr,
legend, listing, main, p, plaintext, pre, summary, xmp, article, aside, h1, h2,
h3, h4, h5, h6, hgroup, nav, section, search, table, caption, colgroup, col,
thead, tbody, tfoot, tr, td, th, dir, dd, dl, dt, menu, ol, ul, li, [dir=ltr i],
[dir=rtl i], [dir=auto i], *|* {
  unicode-bidi: bidi-override;
}
input:not([type=submit i]):not([type=reset i]):not([type=button i]),
textarea {
  unicode-bidi: normal;
}

15.3.6 Sections and headings

@namespace "http://www.w3.org/1999/xhtml";

article, aside, h1, h2, h3, h4, h5, h6, hgroup, nav, section {
  display: block;
}

h1 { margin-block: 0.67em; font-size: 2.00em; font-weight: bold; }
h2 { margin-block: 0.83em; font-size: 1.50em; font-weight: bold; }
h3 { margin-block: 1.00em; font-size: 1.17em; font-weight: bold; }
h4 { margin-block: 1.33em; font-size: 1.00em; font-weight: bold; }
h5 { margin-block: 1.67em; font-size: 0.83em; font-weight: bold; }
h6 { margin-block: 2.33em; font-size: 0.67em; font-weight: bold; }

In the following CSS block, x is shorthand for the following selector: :is(article, aside, nav, section)

@namespace "http://www.w3.org/1999/xhtml";

x h1 { margin-block: 0.83em; font-size: 1.50em; }
x x h1 { margin-block: 1.00em; font-size: 1.17em; }
x x x h1 { margin-block: 1.33em; font-size: 1.00em; }
x x x x h1 { margin-block: 1.67em; font-size: 0.83em; }
x x x x x h1 { margin-block: 2.33em; font-size: 0.67em; }

The shorthand is used to keep this block at least mildly readable.

15.3.7 Lists

@namespace "http://www.w3.org/1999/xhtml";

dir, dd, dl, dt, menu, ol, ul { display: block; }
li { display: list-item; text-align: match-parent; }

dir, dl, menu, ol, ul { margin-block: 1em; }

:is(dir, dl, menu, ol, ul) :is(dir, dl, menu, ol, ul) {
  margin-block: 0;
}

dd { margin-inline-start: 40px; }
dir, menu, ol, ul { padding-inline-start: 40px; }

ol, ul, menu { counter-reset: list-item; }
ol { list-style-type: decimal; }

dir, menu, ul {
  list-style-type: disc;
}
:is(dir, menu, ol, ul) :is(dir, menu, ul) {
  list-style-type: circle;
}
:is(dir, menu, ol, ul) :is(dir, menu, ol, ul) :is(dir, menu, ul) {
  list-style-type: square;
}

The following rules are also expected to apply, as presentational hints:

@namespace "http://www.w3.org/1999/xhtml";

ol[type="1"], li[type="1"] { list-style-type: decimal; }
ol[type=a s], li[type=a s] { list-style-type: lower-alpha; }
ol[type=A s], li[type=A s] { list-style-type: upper-alpha; }
ol[type=i s], li[type=i s] { list-style-type: lower-roman; }
ol[type=I s], li[type=I s] { list-style-type: upper-roman; }
ul[type=none i], li[type=none i] { list-style-type: none; }
ul[type=disc i], li[type=disc i] { list-style-type: disc; }
ul[type=circle i], li[type=circle i] { list-style-type: circle; }
ul[type=square i], li[type=square i] { list-style-type: square; }

When rendering li elements, non-CSS user agents are expected to use the ordinal value of the li element to render the counter in the list item marker.

For CSS user agents, some aspects of rendering list items are defined by the CSS Lists specification. Additionally, the following attribute mappings are expected to apply: [CSSLISTS]

When an li element has a value attribute, and parsing that attribute's value using the rules for parsing integers doesn't generate an error, the user agent is expected to use the parsed value value as a presentational hint for the 'counter-set' property of the form list-item value.

When an ol element has a start attribute or a reversed attribute, or both, the user agent is expected to use the following steps to treat the attributes as a presentational hint for the 'counter-reset' property:

  1. Let value be null.

  2. If the element has a start attribute, then set value to the result of parsing the attribute's value using the rules for parsing integers.

  3. If the element has a reversed attribute, then:

    1. If value is an integer, then increment value by 1 and return reversed(list-item) value.

    2. Otherwise, return reversed(list-item).

      Either the start attribute was absent, or parsing its value resulted in an error.

  4. Otherwise:

    1. If value is an integer, then decrement value by 1 and return list-item value.

    2. Otherwise, there is no presentational hint.

15.3.8 Tables

@namespace "http://www.w3.org/1999/xhtml";

table { display: table; }
caption { display: table-caption; }
colgroup, colgroup[hidden] { display: table-column-group; }
col, col[hidden] { display: table-column; }
thead, thead[hidden] { display: table-header-group; }
tbody, tbody[hidden] { display: table-row-group; }
tfoot, tfoot[hidden] { display: table-footer-group; }
tr, tr[hidden] { display: table-row; }
td, th { display: table-cell; }

colgroup[hidden], col[hidden], thead[hidden], tbody[hidden],
tfoot[hidden], tr[hidden] {
  visibility: collapse;
}

table {
  box-sizing: border-box;
  border-spacing: 2px;
  border-collapse: separate;
  text-indent: initial;
}
td, th { padding: 1px; }
th { font-weight: bold; }

caption { text-align: center; }
thead, tbody, tfoot, table > tr { vertical-align: middle; }
tr, td, th { vertical-align: inherit; }

thead, tbody, tfoot, tr { border-color: inherit; }
table[rules=none i], table[rules=groups i], table[rules=rows i],
table[rules=cols i], table[rules=all i], table[frame=void i],
table[frame=above i], table[frame=below i], table[frame=hsides i],
table[frame=lhs i], table[frame=rhs i], table[frame=vsides i],
table[frame=box i], table[frame=border i],
table[rules=none i] > tr > td, table[rules=none i] > tr > th,
table[rules=groups i] > tr > td, table[rules=groups i] > tr > th,
table[rules=rows i] > tr > td, table[rules=rows i] > tr > th,
table[rules=cols i] > tr > td, table[rules=cols i] > tr > th,
table[rules=all i] > tr > td, table[rules=all i] > tr > th,
table[rules=none i] > thead > tr > td, table[rules=none i] > thead > tr > th,
table[rules=groups i] > thead > tr > td, table[rules=groups i] > thead > tr > th,
table[rules=rows i] > thead > tr > td, table[rules=rows i] > thead > tr > th,
table[rules=cols i] > thead > tr > td, table[rules=cols i] > thead > tr > th,
table[rules=all i] > thead > tr > td, table[rules=all i] > thead > tr > th,
table[rules=none i] > tbody > tr > td, table[rules=none i] > tbody > tr > th,
table[rules=groups i] > tbody > tr > td, table[rules=groups i] > tbody > tr > th,
table[rules=rows i] > tbody > tr > td, table[rules=rows i] > tbody > tr > th,
table[rules=cols i] > tbody > tr > td, table[rules=cols i] > tbody > tr > th,
table[rules=all i] > tbody > tr > td, table[rules=all i] > tbody > tr > th,
table[rules=none i] > tfoot > tr > td, table[rules=none i] > tfoot > tr > th,
table[rules=groups i] > tfoot > tr > td, table[rules=groups i] > tfoot > tr > th,
table[rules=rows i] > tfoot > tr > td, table[rules=rows i] > tfoot > tr > th,
table[rules=cols i] > tfoot > tr > td, table[rules=cols i] > tfoot > tr > th,
table[rules=all i] > tfoot > tr > td, table[rules=all i] > tfoot > tr > th {
  border-color: black;
}

The following rules are also expected to apply, as presentational hints:

@namespace "http://www.w3.org/1999/xhtml";

table[align=left i] { float: left; }
table[align=right i] { float: right; }
table[align=center i] { margin-inline: auto; }
thead[align=absmiddle i], tbody[align=absmiddle i], tfoot[align=absmiddle i],
tr[align=absmiddle i], td[align=absmiddle i], th[align=absmiddle i] {
  text-align: center;
}

caption[align=bottom i] { caption-side: bottom; }
p[align=left i], h1[align=left i], h2[align=left i], h3[align=left i],
h4[align=left i], h5[align=left i], h6[align=left i] {
  text-align: left;
}
p[align=right i], h1[align=right i], h2[align=right i], h3[align=right i],
h4[align=right i], h5[align=right i], h6[align=right i] {
  text-align: right;
}
p[align=center i], h1[align=center i], h2[align=center i], h3[align=center i],
h4[align=center i], h5[align=center i], h6[align=center i] {
  text-align: center;
}
p[align=justify i], h1[align=justify i], h2[align=justify i], h3[align=justify i],
h4[align=justify i], h5[align=justify i], h6[align=justify i] {
  text-align: justify;
}
thead[valign=top i], tbody[valign=top i], tfoot[valign=top i],
tr[valign=top i], td[valign=top i], th[valign=top i] {
  vertical-align: top;
}
thead[valign=middle i], tbody[valign=middle i], tfoot[valign=middle i],
tr[valign=middle i], td[valign=middle i], th[valign=middle i] {
  vertical-align: middle;
}
thead[valign=bottom i], tbody[valign=bottom i], tfoot[valign=bottom i],
tr[valign=bottom i], td[valign=bottom i], th[valign=bottom i] {
  vertical-align: bottom;
}
thead[valign=baseline i], tbody[valign=baseline i], tfoot[valign=baseline i],
tr[valign=baseline i], td[valign=baseline i], th[valign=baseline i] {
  vertical-align: baseline;
}

td[nowrap], th[nowrap] { white-space: nowrap; }

table[rules=none i], table[rules=groups i], table[rules=rows i],
table[rules=cols i], table[rules=all i] {
  border-style: hidden;
  border-collapse: collapse;
}
table[border] { border-style: outset; } /* only if border is not equivalent to zero */
table[frame=void i] { border-style: hidden; }
table[frame=above i] { border-style: outset hidden hidden hidden; }
table[frame=below i] { border-style: hidden hidden outset hidden; }
table[frame=hsides i] { border-style: outset hidden outset hidden; }
table[frame=lhs i] { border-style: hidden hidden hidden outset; }
table[frame=rhs i] { border-style: hidden outset hidden hidden; }
table[frame=vsides i] { border-style: hidden outset; }
table[frame=box i], table[frame=border i] { border-style: outset; }

table[border] > tr > td, table[border] > tr > th,
table[border] > thead > tr > td, table[border] > thead > tr > th,
table[border] > tbody > tr > td, table[border] > tbody > tr > th,
table[border] > tfoot > tr > td, table[border] > tfoot > tr > th {
  /* only if border is not equivalent to zero */
  border-width: 1px;
  border-style: inset;
}
table[rules=none i] > tr > td, table[rules=none i] > tr > th,
table[rules=none i] > thead > tr > td, table[rules=none i] > thead > tr > th,
table[rules=none i] > tbody > tr > td, table[rules=none i] > tbody > tr > th,
table[rules=none i] > tfoot > tr > td, table[rules=none i] > tfoot > tr > th,
table[rules=groups i] > tr > td, table[rules=groups i] > tr > th,
table[rules=groups i] > thead > tr > td, table[rules=groups i] > thead > tr > th,
table[rules=groups i] > tbody > tr > td, table[rules=groups i] > tbody > tr > th,
table[rules=groups i] > tfoot > tr > td, table[rules=groups i] > tfoot > tr > th,
table[rules=rows i] > tr > td, table[rules=rows i] > tr > th,
table[rules=rows i] > thead > tr > td, table[rules=rows i] > thead > tr > th,
table[rules=rows i] > tbody > tr > td, table[rules=rows i] > tbody > tr > th,
table[rules=rows i] > tfoot > tr > td, table[rules=rows i] > tfoot > tr > th {
  border-width: 1px;
  border-style: none;
}
table[rules=cols i] > tr > td, table[rules=cols i] > tr > th,
table[rules=cols i] > thead > tr > td, table[rules=cols i] > thead > tr > th,
table[rules=cols i] > tbody > tr > td, table[rules=cols i] > tbody > tr > th,
table[rules=cols i] > tfoot > tr > td, table[rules=cols i] > tfoot > tr > th {
  border-width: 1px;
  border-block-style: none;
  border-inline-style: solid;
}
table[rules=all i] > tr > td, table[rules=all i] > tr > th,
table[rules=all i] > thead > tr > td, table[rules=all i] > thead > tr > th,
table[rules=all i] > tbody > tr > td, table[rules=all i] > tbody > tr > th,
table[rules=all i] > tfoot > tr > td, table[rules=all i] > tfoot > tr > th {
  border-width: 1px;
  border-style: solid;
}

table[rules=groups i] > colgroup {
  border-inline-width: 1px;
  border-inline-style: solid;
}
table[rules=groups i] > thead,
table[rules=groups i] > tbody,
table[rules=groups i] > tfoot {
  border-block-width: 1px;
  border-block-style: solid;
}

table[rules=rows i] > tr, table[rules=rows i] > thead > tr,
table[rules=rows i] > tbody > tr, table[rules=rows i] > tfoot > tr {
  border-block-width: 1px;
  border-block-style: solid;
}

In quirks mode, the following rules are also expected to apply:

@namespace "http://www.w3.org/1999/xhtml";

table {
  font-weight: initial;
  font-style: initial;
  font-variant: initial;
  font-size: initial;
  line-height: initial;
  white-space: initial;
  text-align: initial;
}

For the purposes of the CSS table model, the col element is expected to be treated as if it was present as many times as its span attribute specifies.

For the purposes of the CSS table model, the colgroup element, if it contains no col element, is expected to be treated as if it had as many such children as its span attribute specifies.

For the purposes of the CSS table model, the colspan and rowspan attributes on td and th elements are expected to provide the special knowledge regarding cells spanning rows and columns.

In HTML documents, the following rules are also expected to apply:

@namespace "http://www.w3.org/1999/xhtml";

:is(table, thead, tbody, tfoot, tr) > form { display: none !important; }

The table element's cellspacing attribute maps to the pixel length property 'border-spacing' on the element.

The table element's cellpadding attribute maps to the pixel length properties 'padding-top', 'padding-right', 'padding-bottom', and 'padding-left' of any td and th elements that have corresponding cells in the table corresponding to the table element.

The table element's height attribute maps to the dimension property 'height' on the table element.

The table element's width attribute maps to the dimension property (ignoring zero) 'width' on the table element.

The col element's width attribute maps to the dimension property 'width' on the col element.

The thead, tbody, and tfoot elements' height attribute maps to the dimension property 'height' on the element.

The tr element's height attribute maps to the dimension property 'height' on the tr element.

The td and th elements' height attributes map to the dimension property (ignoring zero) 'height' on the element.

The td and th elements' width attributes map to the dimension property (ignoring zero) 'width' on the element.

The thead, tbody, tfoot, tr, td, and th elements, when they have an align attribute whose value is an ASCII case-insensitive match for either the string "center" or the string "middle", are expected to center text within themselves, as if they had their 'text-align' property set to 'center' in a presentational hint, and to align descendants to the center.

The thead, tbody, tfoot, tr, td, and th elements, when they have an align attribute whose value is an ASCII case-insensitive match for the string "left", are expected to left-align text within themselves, as if they had their 'text-align' property set to 'left' in a presentational hint, and to align descendants to the left.

The thead, tbody, tfoot, tr, td, and th elements, when they have an align attribute whose value is an ASCII case-insensitive match for the string "right", are expected to right-align text within themselves, as if they had their 'text-align' property set to 'right' in a presentational hint, and to align descendants to the right.

The thead, tbody, tfoot, tr, td, and th elements, when they have an align attribute whose value is an ASCII case-insensitive match for the string "justify", are expected to full-justify text within themselves, as if they had their 'text-align' property set to 'justify' in a presentational hint, and to align descendants to the left.

User agents are expected to have a rule in their user agent style sheet that matches th elements that have a parent node whose computed value for the 'text-align' property is its initial value, whose declaration block consists of just a single declaration that sets the 'text-align' property to the value 'center'.

When a table, thead, tbody, tfoot, tr, td, or th element has a background attribute set to a non-empty value, the new value is expected to be encoding-parsed-and-serialized relative to the element's node document, and if that does not return failure, the user agent is expected to treat the attribute as a presentational hint setting the element's 'background-image' property to the return value.

When a table, thead, tbody, tfoot, tr, td, or th element has a bgcolor attribute set, the new value is expected to be parsed using the rules for parsing a legacy color value, and if that does not return failure, the user agent is expected to treat the attribute as a presentational hint setting the element's 'background-color' property to the resulting color.

When a table element has a bordercolor attribute, its value is expected to be parsed using the rules for parsing a legacy color value, and if that does not return failure, the user agent is expected to treat the attribute as a presentational hint setting the element's 'border-top-color', 'border-right-color', 'border-bottom-color', and 'border-left-color' properties to the resulting color.

The table element's border attribute maps to the pixel length properties 'border-top-width', 'border-right-width', 'border-bottom-width', 'border-left-width' on the element. If the attribute is present but parsing the attribute's value using the rules for parsing non-negative integers generates an error, a default value of 1px is expected to be used for that property instead.

Rules marked "only if border is not equivalent to zero" in the CSS block above is expected to only be applied if the border attribute mentioned in the selectors for the rule is not only present but, when parsed using the rules for parsing non-negative integers, is also found to have a value other than zero or to generate an error.

In quirks mode, a td element or a th element that has a nowrap attribute but also has a width attribute whose value, when parsed using the rules for parsing nonzero dimension values, is found to be a length (not an error or a number classified as a percentage), is expected to have a presentational hint setting the element's 'white-space' property to 'normal', overriding the rule in the CSS block above that sets it to 'nowrap'.

15.3.9 Margin collapsing quirks

A node is substantial if it is a text node that is not inter-element whitespace, or if it is an element node.

A node is blank if it is an element that contains no substantial nodes.

The elements with default margins are the following elements: blockquote, dir, dl, h1, h2, h3, h4, h5, h6, listing, menu, ol, p, plaintext, pre, ul, xmp

In quirks mode, any element with default margins that is the child of a body, td, or th element and has no substantial previous siblings is expected to have a user-agent level style sheet rule that sets its 'margin-block-start' property to zero.

In quirks mode, any element with default margins that is the child of a body, td, or th element, has no substantial previous siblings, and is blank, is expected to have a user-agent level style sheet rule that sets its 'margin-block-end' property to zero also.

In quirks mode, any element with default margins that is the child of a td or th element, has no substantial following siblings, and is blank, is expected to have a user-agent level style sheet rule that sets its 'margin-block-start' property to zero.

In quirks mode, any p element that is the child of a td or th element and has no substantial following siblings, is expected to have a user-agent level style sheet rule that sets its 'margin-block-end' property to zero.

15.3.10 Form controls

@namespace "http://www.w3.org/1999/xhtml";

input, select, button, textarea {
  letter-spacing: initial;
  word-spacing: initial;
  line-height: initial;
  text-transform: initial;
  text-indent: initial;
  text-shadow: initial;
  appearance: auto;
}

input:not([type=image i], [type=range i], [type=checkbox i], [type=radio i]) {
  overflow: clip !important;
  overflow-clip-margin: 0 !important;
}

input, select, textarea {
  text-align: initial;
}

:autofill {
  field-sizing: fixed !important;
}

input:is([type=reset i], [type=button i], [type=submit i]), button {
  text-align: center;
}

input, button {
  display: inline-block;
}

input[type=hidden i], input[type=file i], input[type=image i] {
  appearance: none;
}

input:is([type=radio i], [type=checkbox i], [type=reset i], [type=button i],
[type=submit i], [type=color i], [type=search i]), select, button {
  box-sizing: border-box;
}

textarea { white-space: pre-wrap; }

In quirks mode, the following rules are also expected to apply:

@namespace "http://www.w3.org/1999/xhtml";

input:not([type=image i]), textarea { box-sizing: border-box; }

Each kind of form control is also described in the Widgets section, which describes the look and feel of the control.

For input elements where the type attribute is not in the Hidden state or the Image Button state, and that are being rendered, are expected to act as follows:

15.3.11 The hr element

@namespace "http://www.w3.org/1999/xhtml";

hr {
  color: gray;
  border-style: inset;
  border-width: 1px;
  margin-block: 0.5em;
  margin-inline: auto;
  overflow: hidden;
}

The following rules are also expected to apply, as presentational hints:

@namespace "http://www.w3.org/1999/xhtml";

hr[align=left i] { margin-left: 0; margin-right: auto; }
hr[align=right i] { margin-left: auto; margin-right: 0; }
hr[align=center i] { margin-left: auto; margin-right: auto; }
hr[color], hr[noshade] { border-style: solid; }

If an hr element has either a color attribute or a noshade attribute, and furthermore also has a size attribute, and parsing that attribute's value using the rules for parsing non-negative integers doesn't generate an error, then the user agent is expected to use the parsed value divided by two as a pixel length for presentational hints for the properties 'border-top-width', 'border-right-width', 'border-bottom-width', and 'border-left-width' on the element.

Otherwise, if an hr element has neither a color attribute nor a noshade attribute, but does have a size attribute, and parsing that attribute's value using the rules for parsing non-negative integers doesn't generate an error, then: if the parsed value is one, then the user agent is expected to use the attribute as a presentational hint setting the element's 'border-bottom-width' to 0; otherwise, if the parsed value is greater than one, then the user agent is expected to use the parsed value minus two as a pixel length for presentational hints for the 'height' property on the element.

The width attribute on an hr element maps to the dimension property 'width' on the element.

When an hr element has a color attribute, its value is expected to be parsed using the rules for parsing a legacy color value, and if that does not return failure, the user agent is expected to treat the attribute as a presentational hint setting the element's 'color' property to the resulting color.

15.3.12 The fieldset and legend elements

@namespace "http://www.w3.org/1999/xhtml";

fieldset {
  display: block;
  margin-inline: 2px;
  border: groove 2px ThreeDFace;
  padding-block: 0.35em 0.625em;
  padding-inline: 0.75em;
  min-inline-size: min-content;
}

legend {
  padding-inline: 2px;
}

legend[align=left i] {
  justify-self: left;
}

legend[align=center i] {
  justify-self: center;
}

legend[align=right i] {
  justify-self: right;
}

The fieldset element, when it generates a CSS box, is expected to act as follows:

A fieldset element's rendered legend, if any, is expected to act as follows:

A fieldset element's anonymous fieldset content box is expected to act as follows:

fieldset's margin legend padding legend's margin padding anonymous fieldset content box content
The legend is rendered over the top border, and the top border area reserves vertical space for the legend. The fieldset's top margin starts at the top margin edge of the legend. The legend's horizontal margins, or the 'justify-self' property, gives its horizontal position. The anonymous fieldset content box appears below the legend.

15.4 Replaced elements

The following elements can be replaced elements: audio, canvas, embed, iframe, img, input, object, and video.

15.4.1 Embedded content

The embed, iframe, and video elements are expected to be treated as replaced elements.

A canvas element that represents embedded content is expected to be treated as a replaced element; the contents of such elements are the element's bitmap, if any, or else a transparent black bitmap with the same natural dimensions as the element. Other canvas elements are expected to be treated as ordinary elements in the rendering model.

An object element that represents an image, plugin, or its content navigable is expected to be treated as a replaced element. Other object elements are expected to be treated as ordinary elements in the rendering model.

The audio element, when it is exposing a user interface, is expected to be treated as a replaced element about one line high, as wide as is necessary to expose the user agent's user interface features. When an audio element is not exposing a user interface, the user agent is expected to force its 'display' property to compute to 'none', irrespective of CSS rules.

Whether a video element is exposing a user interface is not expected to affect the size of the rendering; controls are expected to be overlaid above the page content without causing any layout changes, and are expected to disappear when the user does not need them.

When a video element represents a poster frame or frame of video, the poster frame or frame of video is expected to be rendered at the largest size that maintains the aspect ratio of that poster frame or frame of video without being taller or wider than the video element itself, and is expected to be centered in the video element.

Any subtitles or captions are expected to be overlaid directly on top of their video element, as defined by the relevant rendering rules; for WebVTT, those are the rules for updating the display of WebVTT text tracks. [WEBVTT]

When the user agent starts exposing a user interface for a video element, the user agent should run the rules for updating the text track rendering of each of the text tracks in the video element's list of text tracks that are showing and whose text track kind is one of subtitles or captions (e.g., for text tracks based on WebVTT, the rules for updating the display of WebVTT text tracks). [WEBVTT]

Resizing video and canvas elements does not interrupt video playback or clear the canvas.

The following CSS rules are expected to apply:

@namespace "http://www.w3.org/1999/xhtml";

iframe { border: 2px inset; }
video { object-fit: contain; }

15.4.2 Images

User agents are expected to render img elements and input elements whose type attributes are in the Image Button state, according to the first applicable rules from the following list:

If the element represents an image
The user agent is expected to treat the element as a replaced element and render the image according to the rules for doing so defined in CSS.
If the element does not represent an image and either:
The user agent is expected to treat the element as a replaced element whose content is the text that the element represents, if any, optionally alongside an icon indicating that the image is being obtained (if applicable). For input elements, the element is expected to appear button-like to indicate that the element is a button.
If the element is an img element that represents some text and the user agent does not expect this to change
The user agent is expected to treat the element as a non-replaced phrasing element whose content is the text, optionally with an icon indicating that an image is missing, so that the user can request the image be displayed or investigate why it is not rendering. In non-graphical contexts, such an icon should be omitted.
If the element is an img element that represents nothing and the user agent does not expect this to change
The user agent is expected to treat the element as a replaced element whose natural dimensions are 0. (In the absence of further styles, this will cause the element to essentially not be rendered.)
If the element is an input element that does not represent an image and the user agent does not expect this to change
The user agent is expected to treat the element as a replaced element consisting of a button whose content is the element's alternative text. The natural dimensions of the button are expected to be about one line in height and whatever width is necessary to render the text on one line.

The icons mentioned above are expected to be relatively small so as not to disrupt most text but be easily clickable. In a visual environment, for instance, icons could be 16 pixels by 16 pixels square, or 1em by 1em if the images are scalable. In an audio environment, the icon could be a short bleep. The icons are intended to indicate to the user that they can be used to get to whatever options the UA provides for images, and, where appropriate, are expected to provide access to the context menu that would have come up if the user interacted with the actual image.

All animated images with the same absolute URL and the same image data are expected to be rendered synchronized to the same timeline as a group, with the timeline starting at the time of the least recent addition to the group.

In other words, when a second image with the same absolute URL and animated image data is inserted into a document, it jumps to the point in the animation cycle that is currently being displayed by the first image.

When a user agent is to restart the animation for an img element showing an animated image, all animated images with the same absolute URL and the same image data in that img element's node document are expected to restart their animation from the beginning.

The following CSS rules are expected to apply:

@namespace "http://www.w3.org/1999/xhtml";

img:is([sizes="auto" i], [sizes^="auto," i]) {
  contain: size !important;
  contain-intrinsic-size: 300px 150px;
}

The following CSS rules are expected to apply when the Document is in quirks mode:

@namespace "http://www.w3.org/1999/xhtml";

img[align=left i] { margin-right: 3px; }
img[align=right i] { margin-left: 3px; }

15.4.3 Attributes for embedded content and images

The following CSS rules are expected to apply as presentational hints:

@namespace "http://www.w3.org/1999/xhtml";

iframe[frameborder='0'], iframe[frameborder=no i] { border: none; }

embed[align=left i], iframe[align=left i], img[align=left i],
input[type=image i][align=left i], object[align=left i] {
  float: left;
}

embed[align=right i], iframe[align=right i], img[align=right i],
input[type=image i][align=right i], object[align=right i] {
  float: right;
}

embed[align=top i], iframe[align=top i], img[align=top i],
input[type=image i][align=top i], object[align=top i] {
  vertical-align: top;
}

embed[align=baseline i], iframe[align=baseline i], img[align=baseline i],
input[type=image i][align=baseline i], object[align=baseline i] {
  vertical-align: baseline;
}

embed[align=texttop i], iframe[align=texttop i], img[align=texttop i],
input[type=image i][align=texttop i], object[align=texttop i] {
  vertical-align: text-top;
}

embed[align=absmiddle i], iframe[align=absmiddle i], img[align=absmiddle i],
input[type=image i][align=absmiddle i], object[align=absmiddle i],
embed[align=abscenter i], iframe[align=abscenter i], img[align=abscenter i],
input[type=image i][align=abscenter i], object[align=abscenter i] {
  vertical-align: middle;
}

embed[align=bottom i], iframe[align=bottom i], img[align=bottom i],
input[type=image i][align=bottom i], object[align=bottom i] {
  vertical-align: bottom;
}

When an embed, iframe, img, or object element, or an input element whose type attribute is in the Image Button state, has an align attribute whose value is an ASCII case-insensitive match for the string "center" or the string "middle", the user agent is expected to act as if the element's 'vertical-align' property was set to a value that aligns the vertical middle of the element with the parent element's baseline.

The hspace attribute of embed, img, or object elements, and input elements with a type attribute in the Image Button state, maps to the dimension properties 'margin-left' and 'margin-right' on the element.

The vspace attribute of embed, img, or object elements, and input elements with a type attribute in the Image Button state, maps to the dimension properties 'margin-top' and 'margin-bottom' on the element.

When an img element, object element, or input element with a type attribute in the Image Button state has a border attribute whose value, when parsed using the rules for parsing non-negative integers, is found to be a number greater than zero, the user agent is expected to use the parsed value for eight presentational hints: four setting the parsed value as a pixel length for the element's 'border-top-width', 'border-right-width', 'border-bottom-width', and 'border-left-width' properties, and four setting the element's 'border-top-style', 'border-right-style', 'border-bottom-style', and 'border-left-style' properties to the value 'solid'.

The width and height attributes on an img element's dimension attribute source map to the dimension properties 'width' and 'height' on the img element respectively. They similarly map to the aspect-ratio property (using dimension rules) of the img element.

The width and height attributes on embed, iframe, object, and video elements, and input elements with a type attribute in the Image Button state and that either represents an image or that the user expects will eventually represent an image, map to the dimension properties 'width' and 'height' on the element respectively.

The width and height attributes map to the aspect-ratio property (using dimension rules) on img and video elements, and input elements with a type attribute in the Image Button state.

The width and height attributes map to the aspect-ratio property on canvas elements.

15.4.4 Image maps

Shapes on an image map are expected to act, for the purpose of the CSS cascade, as elements independent of the original area element that happen to match the same style rules but inherit from the img or object element.

For the purposes of the rendering, only the 'cursor' property is expected to have any effect on the shape.

Thus, for example, if an area element has a style attribute that sets the 'cursor' property to 'help', then when the user designates that shape, the cursor would change to a Help cursor.

Similarly, if an area element had a CSS rule that set its 'cursor' property to 'inherit' (or if no rule setting the 'cursor' property matched the element at all), the shape's cursor would be inherited from the img or object element of the image map, not from the parent of the area element.

15.5 Widgets

15.5.1 Native appearance

The CSS Basic User Interface specification calls elements that can have a native appearance widgets, and defines whether to use that native appearance depending on the 'appearance' property. That logic, in turn, depends on whether on whether each the element is classified as a devolvable widget or non-devolvable widget. This section defines which elements match these concepts for HTML, what their native appearance is, and any particularity of their devolved state or primitive appearance. [CSSUI]

The following elements can have a native appearance for the purpose of the CSS 'appearance' property.

15.5.2 Writing mode

Several widgets have their rendering controlled by the 'writing-mode' CSS property. For the purposes of those widgets, we have the following definitions.

A horizontal writing mode is when resolving the 'writing-mode' property of the control results in a computed value of 'horizontal-tb'.

A vertical writing mode is when resolving the 'writing-mode' property of the control results in a computed value of either 'vertical-rl', 'vertical-lr', 'sideways-rl' or 'sideways-lr'.

15.5.3 Button layout

When an element uses button layout, it is a devolvable widget, and it's native appearance is that of a button.

Button layout is as follows:

Need to define the expected primitive appearance.

15.5.4 The button element

The button element, when it generates a CSS box, is expected to depict a button and to use button layout whose anonymous button content box's contents (if there is an anonymous button content box) are the child boxes the element's box would otherwise have.

15.5.5 The details and summary elements

@namespace "http://www.w3.org/1999/xhtml";

details, summary {
  display: block;
}
details > summary:first-of-type {
  display: list-item;
  counter-increment: list-item 0;
  list-style: disclosure-closed inside;
}
details[open] > summary:first-of-type {
  list-style-type: disclosure-open;
}

The details element is expected to have an internal shadow tree with three child elements:

  1. The first child element is a slot that is expected to take the details element's first summary element child, if any. This element has a single child summary element called the default summary which has text content that is implementation-defined (and probably locale-specific).

    The summary element that this slot represents is expected to allow the user to request the details be shown or hidden.

  2. The second child element is a slot that is expected to take the details element's remaining descendants, if any. This element has no contents.

    This element is expected to match the '::details-content' pseudo-element.

    This element is expected to have its style attribute set to "display: block; content-visibility: hidden;" when the details element does not have an open attribute. When it does have the open attribute, the style attribute is expected to be set to "display: block;".

    Because the slots are hidden inside a shadow tree, this style attribute is not directly visible to author code. Its impacts, however, are visible. Notably, the choice of content-visibility: hidden instead of, e.g., display: none, impacts the results of various APIs that query layout information.

  3. The third child element is either a link or style element with the following styles for the default summary:

    :host summary {
  display: list-item;
  counter-increment: list-item 0;
  list-style: disclosure-closed inside;
}
:host([open]) summary {
  list-style-type: disclosure-open;
}

    The position of this child element relative to the other two is not observable. This means that implementations might have it in a different order relative to its siblings. Implementations might even associate the style with the shadow tree using a mechanism that is not an element.

The structure of this shadow tree is observable through the ways that the children of the details element and the '::details-content' pseudo-element respond to CSS styles.

15.5.6 The input element as a text entry widget

An input element whose type attribute is in the Text, Telephone, URL, or Email state, is a devolvable widget. Its expected native appearance is to render as an 'inline-block' box depicting a one-line text control.

An input element whose type attribute is in the Search state is a devolvable widget. Its expected native appearance is to render as an 'inline-block' box depicting a one-line text control. If the computed value of the element's 'appearance' property is not 'textfield', it may have a distinct style indicating that it is a search field.

An input element whose type attribute is in the Password state is a devolvable widget. Its expected native appearance is to render as an 'inline-block' box depicting a one-line text control that obscures data entry.

For input elements whose type attribute is in one of the above states, the used value of the 'line-height' property must be a length value that is no smaller than what the used value would be for 'line-height: normal'.

The used value will not be the actual keyword 'normal'. Also, this rule does not affect the computed value.

If these text controls provide a text selection, then, when the user changes the current selection, the user agent is expected to queue an element task on the user interaction task source given the input element to fire an event named select at the element, with the bubbles attribute initialized to true.

An input element whose type attribute is in one of the above states is an element with default preferred size, and user agents are expected to apply the 'field-sizing' CSS property to the element. User agents are expected to determine the inline size of its intrinsic size by the following steps:

  1. If the 'field-sizing' property on the element has a computed value of 'content', the inline size is determined by the text which the element shows. The text is either a value or a short hint specified by the placeholder attribute. User agents may take the text caret size into account in the inline size.

  2. If the element has a size attribute, and parsing that attribute's value using the rules for parsing non-negative integers doesn't generate an error, return the value obtained from applying the converting a character width to pixels algorithm to the value of the attribute.

  3. Otherwise, return the value obtained from applying the converting a character width to pixels algorithm to the number 20.

The converting a character width to pixels algorithm returns (size-1)×avg + max, where size is the character width to convert, avg is the average character width of the primary font for the element for which the algorithm is being run, in pixels, and max is the maximum character width of that same font, also in pixels. (The element's 'letter-spacing' property does not affect the result.)

These text controls are expected to be scroll containers and support scrolling in the inline axis, but not the block axis.

Need to detail the expected native appearance and primitive appearance.

15.5.7 The input element as domain-specific widgets

An input element whose type attribute is in the Date state is a devolvable widget expected to render as an 'inline-block' box depicting a date control.

An input element whose type attribute is in the Month state is a devolvable widget expected to render as an 'inline-block' box depicting a month control.

An input element whose type attribute is in the Week state is a devolvable widget expected to render as an 'inline-block' box depicting a week control.

An input element whose type attribute is in the Time state is a devolvable widget expected to render as an 'inline-block' box depicting a time control.

An input element whose type attribute is in the Local Date and Time state is a devolvable widget expected to render as an 'inline-block' box depicting a local date and time control.

An input element whose type attribute is in the Number state is a devolvable widget expected to render as an 'inline-block' box depicting a number control.

An input element whose type attribute is in the Number state is an element with default preferred size, and user agents are expected to apply the 'field-sizing' CSS property to the element. The block size of the intrinsic size is about one line high. If the 'field-sizing' property on the element has a computed value of 'content', the inline size of the intrinsic size is expected to be about as wide as necessary to show the current value. Otherwise, the inline size of the intrinsic size is expected to be about as wide as necessary to show the widest possible value.

An input element whose type attribute is in the Date, Month, Week, Time, or Local Date and Time state, is expected to be about one line high, and about as wide as necessary to show the widest possible value.

Need to detail the expected native appearance and primitive appearance.

15.5.8 The input element as a range control

An input element whose type attribute is in the Range state is a non-devolvable widget. Its expected native appearance is to render as an 'inline-block' box depicting a slider control.

When this control has a horizontal writing mode, the control is expected to be a horizontal slider. Its lowest value is on the right if the 'direction' property has a computed value of 'rtl', and on the left otherwise. When this control has a vertical writing mode, it is expected to be a vertical slider. Its lowest value is on the bottom if the 'direction' property has a computed value of 'rtl', and on the top otherwise.

Predefined suggested values (provided by the list attribute) are expected to be shown as tick marks on the slider, which the slider can snap to.

Need to detail the expected primitive appearance.

15.5.9 The input element as a color well

An input element whose type attribute is in the Color state is expected to depict a color well, which, when activated, provides the user with a color picker (e.g. a color wheel or color palette) from which the color can be changed. The element, when it generates a CSS box, is expected to use button layout, that has no child boxes of the anonymous button content box. The anonymous button content box is expected to have a presentational hint setting the 'background-color' property to the element's value.

Predefined suggested values (provided by the list attribute) are expected to be shown in the color picker interface, not on the color well itself.

Need to detail the expected native appearance and primitive appearance.

15.5.10 The input element as a checkbox and radio button widgets

An input element whose type attribute is in the Checkbox state is a non-devolvable widget expected to render as an 'inline-block' box containing a single checkbox control, with no label.

Need to detail the expected native appearance and primitive appearance.

An input element whose type attribute is in the Radio Button state is a non-devolvable widget expected to render as an 'inline-block' box containing a single radio button control, with no label.

Need to detail the expected native appearance and primitive appearance.

15.5.11 The input element as a file upload control

An input element whose type attribute is in the File Upload state, when it generates a CSS box, is expected to render as an 'inline-block' box containing a span of text giving the filename(s) of the selected files, if any, followed by a button that, when activated, provides the user with a file picker from which the selection can be changed. The button is expected to use button layout and match the '::file-selector-button' pseudo-element. The contents of its anonymous button content box are expected to be implementation-defined (and possibly locale-specific) text, for example "Choose file".

User agents may handle an input element whose type attribute is in the File Upload state as an element with default preferred size, and user agents may apply the 'field-sizing' CSS property to the element. If the 'field-sizing' property on the element has a computed value of 'content', the intrinsic size of the element is expected to depend on its content such as the '::file-selector-button' pseudo-element and chosen file names.

15.5.12 The input element as a button

An input element whose type attribute is in the Submit Button, Reset Button, or Button state, when it generates a CSS box, is expected to depict a button and use button layout and the contents of the anonymous button content box are expected to be the text of the element's value attribute, if any, or text derived from the element's type attribute in an implementation-defined (and probably locale-specific) fashion, if not.

15.5.13 The marquee element

@namespace "http://www.w3.org/1999/xhtml";

marquee {
  display: inline-block;
  text-align: initial;
  overflow: hidden !important;
}

The marquee element, while turned on, is expected to render in an animated fashion according to its attributes as follows:

If the element's behavior attribute is in the scroll state

Slide the contents of the element in the direction described by the direction attribute as defined below, such that it begins off the start side of the marquee, and ends flush with the inner end side.

For example, if the direction attribute is left (the default), then the contents would start such that their left edge are off the side of the right edge of the marquee's content area, and the contents would then slide up to the point where the left edge of the contents are flush with the left inner edge of the marquee's content area.

Once the animation has ended, the user agent is expected to increment the marquee current loop index. If the element is still turned on after this, then the user agent is expected to restart the animation.

If the element's behavior attribute is in the slide state

Slide the contents of the element in the direction described by the direction attribute as defined below, such that it begins off the start side of the marquee, and ends off the end side of the marquee.

For example, if the direction attribute is left (the default), then the contents would start such that their left edge are off the side of the right edge of the marquee's content area, and the contents would then slide up to the point where the right edge of the contents are flush with the left inner edge of the marquee's content area.

Once the animation has ended, the user agent is expected to increment the marquee current loop index. If the element is still turned on after this, then the user agent is expected to restart the animation.

If the element's behavior attribute is in the alternate state

When the marquee current loop index is even (or zero), slide the contents of the element in the direction described by the direction attribute as defined below, such that it begins flush with the start side of the marquee, and ends flush with the end side of the marquee.

When the marquee current loop index is odd, slide the contents of the element in the opposite direction than that described by the direction attribute as defined below, such that it begins flush with the end side of the marquee, and ends flush with the start side of the marquee.

For example, if the direction attribute is left (the default), then the contents would with their right edge flush with the right inner edge of the marquee's content area, and the contents would then slide up to the point where the left edge of the contents are flush with the left inner edge of the marquee's content area.

Once the animation has ended, the user agent is expected to increment the marquee current loop index. If the element is still turned on after this, then the user agent is expected to continue the animation.

The direction attribute has the meanings described in the following table:

direction attribute state Direction of animation Start edge End edge Opposite direction
left ← Right to left Right Left → Left to Right
right → Left to Right Left Right ← Right to left
up ↑ Up (Bottom to Top) Bottom Top ↓ Down (Top to Bottom)
down ↓ Down (Top to Bottom) Top Bottom ↑ Up (Bottom to Top)

In any case, the animation should proceed such that there is a delay given by the marquee scroll interval between each frame, and such that the content moves at most the distance given by the marquee scroll distance with each frame.

When a marquee element has a bgcolor attribute set, the value is expected to be parsed using the rules for parsing a legacy color value, and if that does not return failure, the user agent is expected to treat the attribute as a presentational hint setting the element's 'background-color' property to the resulting color.

The width and height attributes on a marquee element map to the dimension properties 'width' and 'height' on the element respectively.

The natural height of a marquee element with its direction attribute in the up or down states is 200 CSS pixels.

The vspace attribute of a marquee element maps to the dimension properties 'margin-top' and 'margin-bottom' on the element. The hspace attribute of a marquee element maps to the dimension properties 'margin-left' and 'margin-right' on the element.

15.5.14 The meter element

@namespace "http://www.w3.org/1999/xhtml";

meter { appearance: auto; }

The meter element is a devolvable widget. Its expected native appearance is to render as an 'inline-block' box with a 'block-size' of '1em' and a 'inline-size' of '5em', a 'vertical-align' of '-0.2em', and with its contents depicting a gauge.

When this element has a horizontal writing mode, the depiction is expected to be of a horizontal gauge. Its minimum value is on the right if the 'direction' property has a computed value of 'rtl', and on the left otherwise. When this element has a vertical writing mode, it is expected to depict a vertical gauge. Its minimum value is on the bottom if the 'direction' property has a computed value of 'rtl', and on the top otherwise.

User agents are expected to use a presentation consistent with platform conventions for gauges, if any.

Requirements for what must be depicted in the gauge are included in the definition of the meter element.

Need to detail the expected primitive appearance.

15.5.15 The progress element

@namespace "http://www.w3.org/1999/xhtml";

progress { appearance: auto; }

The progress element is a devolvable widget. Its expected native appearance is to render as an 'inline-block' box with a 'block-size' of '1em' and a 'inline-size' of '10em', and a 'vertical-align' of '-0.2em'.

When the this element has a horizontal writing mode, the element is expected to be depicted as a horizontal progress bar. The start is on the right and the end is on the left if the 'direction' property on this element has a computed value of 'rtl', and with the start on the left and the end on the right otherwise. When this element has a vertical writing mode, it is expected to be depicted as a vertical progress bar. The start is on the bottom and the end is on the top if the 'direction' property on this element has a computed value of 'rtl', and with the start on the top and the end on the bottom otherwise.

User agents are expected to use a presentation consistent with platform conventions for progress bars. In particular, user agents are expected to use different presentations for determinate and indeterminate progress bars. User agents are also expected to vary the presentation based on the dimensions of the element.

Requirements for how to determine if the progress bar is determinate or indeterminate, and what progress a determinate progress bar is to show, are included in the definition of the progress element.

Need to detail the expected primitive appearance.

15.5.16 The select element

The select element is an element with default preferred size, and user agents are expected to apply the 'field-sizing' CSS property to select elements.

A select element is either a list box or a drop-down box, depending on its attributes.

A select element whose multiple attribute is present is expected to render as a multi-select list box.

A select element whose multiple attribute is absent, and whose display size is greater than 1, is expected to render as a single-select list box.

When the element renders as a list box, it is a devolvable widget expected to render as an 'inline-block' box. The inline size of its intrinsic size is the width of the select's labels plus the width of a scrollbar. The block size of its intrinsic size is determined by the following steps:

  1. If the 'field-sizing' property on the element has a computed value of 'content', return the height necessary to contain all rows for items.

  2. If the size attribute is absent or it has no valid value, return the height necessary to contain four rows.

  3. Otherwise, return the height necessary to contain as many rows for items as given by the element's display size.

A select element whose multiple attribute is absent, and whose display size is 1, is expected to render as an 'inline-block' one-line drop-down box. The inline size of its intrinsic size is the width of the select's labels. If the 'field-sizing' property on the element has a computed value of 'content', the inline size of the intrinsic size depends on the shown text. The shown text is typically the label of an option of which selectedness is set to true.

When the element renders as a drop-down box, it is a devolvable widget. Its appearance in the devolved state, as well as its appearance when the computed value of the element's 'appearance' property is 'menulist-button', is that of a drop-down box, including a "drop-down button", but not necessarily rendered using a native control of the host operating system. In such a state, CSS properties such as 'color', 'background-color', and 'border' should not be disregarded (as is generally permissible when rendering an element according to its native appearance).

In either case (list box or drop-down box), the element's items are expected to be the element's list of options, with the element's optgroup element children providing headers for groups of options where applicable.

An optgroup element is expected to be rendered by displaying the element's label attribute.

An option element is expected to be rendered by displaying the element's label, indented under its optgroup element if it has one.

Each sequence of one or more child hr element siblings may be rendered as a single separator.

The width of the select's labels is the wider of the width necessary to render the widest optgroup, and the width necessary to render the widest option element in the element's list of options (including its indent, if any).

If a select element contains a placeholder label option, the user agent is expected to render that option in a manner that conveys that it is a label, rather than a valid option of the control. This can include preventing the placeholder label option from being explicitly selected by the user. When the placeholder label option's selectedness is true, the control is expected to be displayed in a fashion that indicates that no valid option is currently selected.

User agents are expected to render the labels in a select in such a manner that any alignment remains consistent whether the label is being displayed as part of the page or in a menu control.

Need to detail the expected native appearance and primitive appearance.

15.5.17 The textarea element

The textarea element is a devolvable widget expected to render as an 'inline-block' box depicting a multiline text control. If this multiline text control provides a selection, then, when the user changes the current selection, the user agent is expected to queue an element task on the user interaction task source given the textarea element to fire an event named select at the element, with the bubbles attribute initialized to true.

The textarea element is an element with default preferred size, and user agents are expected to apply the 'field-sizing' CSS property to textarea elements.

If the 'field-sizing' property on the element has a computed value of 'content', the intrinsic size is determined from the text which the element shows. The text is either a raw value or a short hint specified by the placeholder attribute. User agents may take the text caret size into account in the intrinsic size. Otherwise, its intrinsic size is computed from textarea effective width and textarea effective height (as defined below).

The textarea effective width of a textarea element is size×avg + sbw, where size is the element's character width, avg is the average character width of the primary font of the element, in CSS pixels, and sbw is the width of a scrollbar, in CSS pixels. (The element's 'letter-spacing' property does not affect the result.)

The textarea effective height of a textarea element is the height in CSS pixels of the number of lines specified the element's character height, plus the height of a scrollbar in CSS pixels.

User agents are expected to apply the 'white-space' CSS property to textarea elements. For historical reasons, if the element has a wrap attribute whose value is an ASCII case-insensitive match for the string "off", then the user agent is expected to treat the attribute as a presentational hint setting the element's 'white-space' property to 'pre'.

Need to detail the expected native appearance and primitive appearance.

15.6 Frames and framesets

User agents are expected to render frameset elements as a box with the height and width of the viewport, with a surface rendered according to the following layout algorithm:

  1. The cols and rows variables are lists of zero or more pairs consisting of a number and a unit, the unit being one of percentage, relative, and absolute.

    Use the rules for parsing a list of dimensions to parse the value of the element's cols attribute, if there is one. Let cols be the result, or an empty list if there is no such attribute.

    Use the rules for parsing a list of dimensions to parse the value of the element's rows attribute, if there is one. Let rows be the result, or an empty list if there is no such attribute.

  2. For any of the entries in cols or rows that have the number zero and the unit relative, change the entry's number to one.

  3. If cols has no entries, then add a single entry consisting of the value 1 and the unit relative to cols.

    If rows has no entries, then add a single entry consisting of the value 1 and the unit relative to rows.

  4. Invoke the algorithm defined below to convert a list of dimensions to a list of pixel values using cols as the input list, and the width of the surface that the frameset is being rendered into, in CSS pixels, as the input dimension. Let sized cols be the resulting list.

    Invoke the algorithm defined below to convert a list of dimensions to a list of pixel values using rows as the input list, and the height of the surface that the frameset is being rendered into, in CSS pixels, as the input dimension. Let sized rows be the resulting list.

  5. Split the surface into a grid of w×h rectangles, where w is the number of entries in sized cols and h is the number of entries in sized rows.

    Size the columns so that each column in the grid is as many CSS pixels wide as the corresponding entry in the sized cols list.

    Size the rows so that each row in the grid is as many CSS pixels high as the corresponding entry in the sized rows list.

  6. Let children be the list of frame and frameset elements that are children of the frameset element for which the algorithm was invoked.

  7. For each row of the grid of rectangles created in the previous step, from top to bottom, run these substeps:

    1. For each rectangle in the row, from left to right, run these substeps:

      1. If there are any elements left in children, take the first element in the list, and assign it to the rectangle.

        If this is a frameset element, then recurse the entire frameset layout algorithm for that frameset element, with the rectangle as the surface.

        Otherwise, it is a frame element; render its content navigable, positioned and sized to fit the rectangle.

      2. If there are any elements left in children, remove the first element from children.

  8. If the frameset element has a border, draw an outer set of borders around the rectangles, using the element's frame border color.

    For each rectangle, if there is an element assigned to that rectangle, and that element has a border, draw an inner set of borders around that rectangle, using the element's frame border color.

    For each (visible) border that does not abut a rectangle that is assigned a frame element with a noresize attribute (including rectangles in further nested frameset elements), the user agent is expected to allow the user to move the border, resizing the rectangles within, keeping the proportions of any nested frameset grids.

    A frameset or frame element has a border if the following algorithm returns true:

    1. If the element has a frameborder attribute whose value is not the empty string and whose first character is either a U+0031 DIGIT ONE (1) character, a U+0079 LATIN SMALL LETTER Y character (y), or a U+0059 LATIN CAPITAL LETTER Y character (Y), then return true.

    2. Otherwise, if the element has a frameborder attribute, return false.

    3. Otherwise, if the element has a parent element that is a frameset element, then return true if that element has a border, and false if it does not.

    4. Otherwise, return true.

    The frame border color of a frameset or frame element is the color obtained from the following algorithm:

    1. If the element has a bordercolor attribute, and applying the rules for parsing a legacy color value to that attribute's value does not return failure, then return the color so obtained.

    2. Otherwise, if the element has a parent element that is a frameset element, then return the frame border color of that element.

    3. Otherwise, return gray.

The algorithm to convert a list of dimensions to a list of pixel values consists of the following steps:

  1. Let input list be the list of numbers and units passed to the algorithm.

    Let output list be a list of numbers the same length as input list, all zero.

    Entries in output list correspond to the entries in input list that have the same position.

  2. Let input dimension be the size passed to the algorithm.

  3. Let count percentage be the number of entries in input list whose unit is percentage.

    Let total percentage be the sum of all the numbers in input list whose unit is percentage.

    Let count relative be the number of entries in input list whose unit is relative.

    Let total relative be the sum of all the numbers in input list whose unit is relative.

    Let count absolute be the number of entries in input list whose unit is absolute.

    Let total absolute be the sum of all the numbers in input list whose unit is absolute.

    Let remaining space be the value of input dimension.

  4. If total absolute is greater than remaining space, then for each entry in input list whose unit is absolute, set the corresponding value in output list to the number of the entry in input list multiplied by remaining space and divided by total absolute. Then, set remaining space to zero.

    Otherwise, for each entry in input list whose unit is absolute, set the corresponding value in output list to the number of the entry in input list. Then, decrement remaining space by total absolute.

  5. If total percentage multiplied by the input dimension and divided by 100 is greater than remaining space, then for each entry in input list whose unit is percentage, set the corresponding value in output list to the number of the entry in input list multiplied by remaining space and divided by total percentage. Then, set remaining space to zero.

    Otherwise, for each entry in input list whose unit is percentage, set the corresponding value in output list to the number of the entry in input list multiplied by the input dimension and divided by 100. Then, decrement remaining space by total percentage multiplied by the input dimension and divided by 100.

  6. For each entry in input list whose unit is relative, set the corresponding value in output list to the number of the entry in input list multiplied by remaining space and divided by total relative.

  7. Return output list.

User agents working with integer values for frame widths (as opposed to user agents that can lay frames out with subpixel accuracy) are expected to distribute the remainder first to the last entry whose unit is relative, then equally (not proportionally) to each entry whose unit is percentage, then equally (not proportionally) to each entry whose unit is absolute, and finally, failing all else, to the last entry.

The contents of a frame element that does not have a frameset parent are expected to be rendered as transparent black; the user agent is expected to not render its content navigable in this case, and its content navigable is expected to have a viewport with zero width and zero height.

15.7 Interactive media

15.7.1 Links, forms, and navigation

User agents are expected to allow the user to control aspects of hyperlink activation and form submission, such as which navigable is to be used for the subsequent navigation.

User agents are expected to allow users to discover the destination of hyperlinks and of forms before triggering their navigation.

User agents are expected to inform the user of whether a hyperlink includes hyperlink auditing, and to let them know at a minimum which domains will be contacted as part of such auditing.

User agents may allow users to navigate navigables to the URLs indicated by the cite attributes on q, blockquote, ins, and del elements.

User agents may surface hyperlinks created by link elements in their user interface, as discussed previously.

15.7.2 The title attribute

User agents are expected to expose the advisory information of elements upon user request, and to make the user aware of the presence of such information.

On interactive graphical systems where the user can use a pointing device, this could take the form of a tooltip. When the user is unable to use a pointing device, then the user agent is expected to make the content available in some other fashion, e.g. by making the element a focusable area and always displaying the advisory information of the currently focused element, or by showing the advisory information of the elements under the user's finger on a touch device as the user pans around the screen.

U+000A LINE FEED (LF) characters are expected to cause line breaks in the tooltip; U+0009 CHARACTER TABULATION (tab) characters are expected to render as a nonzero horizontal shift that lines up the next glyph with the next tab stop, with tab stops occurring at points that are multiples of 8 times the width of a U+0020 SPACE character.

For example, a visual user agent could make elements with a title attribute focusable, and could make any focused element with a title attribute show its tooltip under the element while the element has focus. This would allow a user to tab around the document to find all the advisory text.

As another example, a screen reader could provide an audio cue when reading an element with a tooltip, with an associated key to read the last tooltip for which a cue was played.

15.7.3 Editing hosts

The current text editing caret (i.e. the active range, if it is empty and in an editing host), if any, is expected to act like an inline replaced element with the vertical dimensions of the caret and with zero width for the purposes of the CSS rendering model.

This means that even an empty block can have the caret inside it, and that when the caret is in such an element, it prevents margins from collapsing through the element.

15.7.4 Text rendered in native user interfaces

User agents are expected to honor the Unicode semantics of text that is exposed in user interfaces, for example supporting the bidirectional algorithm in text shown in dialogs, title bars, popup menus, and tooltips. Text from the contents of elements is expected to be rendered in a manner that honors the directionality of the element from which the text was obtained. Text from attributes is expected to be rendered in a manner that honours the directionality of the attribute.

Consider the following markup, which has Hebrew text asking for a programming language, the languages being text for which a left-to-right direction is important given the punctuation in some of their names:

<p dir="rtl" lang="he">
 <label>
  בחר שפת תכנות:
  <select>
   <option dir="ltr">C++</option>
   <option dir="ltr">C#</option>
   <option dir="ltr">FreePascal</option>
   <option dir="ltr">F#</option>
  </select>
 </label>
</p>

If the select element was rendered as a drop down box, a correct rendering would ensure that the punctuation was the same both in the drop down, and in the box showing the current selection.

The directionality of attributes depends on the attribute and on the element's dir attribute, as the following example demonstrates. Consider this markup:

<table>
 <tr>
  <th abbr="(א" dir=ltr>A
  <th abbr="(א" dir=rtl>A
  <th abbr="(א" dir=auto>A
</table>

If the abbr attributes are rendered, e.g. in a tooltip or other user interface, the first will have a left parenthesis (because the direction is 'ltr'), the second will have a right parenthesis (because the direction is 'rtl'), and the third will have a right parenthesis (because the direction is determined from the attribute value to be 'rtl').

However, if instead the attribute was not a directionality-capable attribute, the results would be different:

<table>
 <tr>
  <th data-abbr="(א" dir=ltr>A
  <th data-abbr="(א" dir=rtl>A
  <th data-abbr="(א" dir=auto>A
</table>

In this case, if the user agent were to expose the data-abbr attribute in the user interface (e.g. in a debugging environment), the last case would be rendered with a left parenthesis, because the direction would be determined from the element's contents.

A string provided by a script (e.g. the argument to window.alert()) is expected to be treated as an independent set of one or more bidirectional algorithm paragraphs when displayed, as defined by the bidirectional algorithm, including, for instance, supporting the paragraph-breaking behavior of U+000A LINE FEED (LF) characters. For the purposes of determining the paragraph level of such text in the bidirectional algorithm, this specification does not provide a higher-level override of rules P2 and P3. [BIDI]

When necessary, authors can enforce a particular direction for a given paragraph by starting it with the Unicode U+200E LEFT-TO-RIGHT MARK or U+200F RIGHT-TO-LEFT MARK characters.

Thus, the following script:

alert('\u05DC\u05DE\u05D3 HTML \u05D4\u05D9\u05D5\u05DD!')

...would always result in a message reading "למד LMTH היום!" (not "דמל HTML םויה!"), regardless of the language of the user agent interface or the direction of the page or any of its elements.

For a more complex example, consider the following script:

/* Warning: this script does not handle right-to-left scripts correctly */
var s;
if (s = prompt('What is your name?')) {
  alert(s + '! Ok, Fred, ' + s + ', and Wilma will get the car.');
}

When the user enters "Kitty", the user agent would alert "Kitty! Ok, Fred, Kitty, and Wilma will get the car.". However, if the user enters "لا أفهم", then the bidirectional algorithm will determine that the direction of the paragraph is right-to-left, and so the output will be the following unintended mess: "لا أفهم! derF ,kO, لا أفهم, rac eht teg lliw amliW dna."

To force an alert that starts with user-provided text (or other text of unknown directionality) to render left-to-right, the string can be prefixed with a U+200E LEFT-TO-RIGHT MARK character:

var s;
if (s = prompt('What is your name?')) {
  alert('\u200E' + s + '! Ok, Fred, ' + s + ', and Wilma will get the car.');
}

User agents are expected to allow the user to request the opportunity to obtain a physical form (or a representation of a physical form) of a Document. For example, selecting the option to print a page or convert it to PDF format. [PDF]

When the user actually obtains a physical form (or a representation of a physical form) of a Document, the user agent is expected to create a new rendering of the Document for the print media.

15.9 Unstyled XML documents

HTML user agents may, in certain circumstances, find themselves rendering non-HTML documents that use vocabularies for which they lack any built-in knowledge. This section provides for a way for user agents to handle such documents in a somewhat useful manner.

While a Document is an unstyled document, the user agent is expected to render an unstyled document view.

A Document is an unstyled document while it matches the following conditions:

An unstyled document view is one where the DOM is not rendered according to CSS (which would, since there are no applicable styles in this context, just result in a wall of text), but is instead rendered in a manner that is useful for a developer. This could consist of just showing the Document object's source, maybe with syntax highlighting, or it could consist of displaying just the DOM tree, or simply a message saying that the page is not a styled document.

If a Document stops being an unstyled document, then the conditions above stop applying, and thus a user agent following these requirements will switch to using the regular CSS rendering.