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<h1>CSS Basic User Interface Module Level 4</h1>
<pre class='metadata'>
ED: http://dev.w3.org/csswg/css-ui-4/
Previous Version: http://www.w3.org/TR/css3-ui/
Shortname: css-ui
Level: 4
Group: csswg
!Issue Tracking: https://wiki.csswg.org/spec/css4-ui#css4-ui-issues-list
Status: ED
Work Status: Exploring
Editor: Florian Rivoal, Invited Expert, florian@rivoal.net, http://florian.rivoal.net
Ignored Terms: box-sizing, resize, text-overflow, caret-color, nav-up, nav-down, nav-left, nav-right
Link Defaults: css-position-3 (property) position
Link Defaults: css21 (property) float
Link Defaults: css21 (property) clear
Link Defaults: selectors-4 (selector) :checked
Link Defaults: selectors-4 (selector) :enabled
Link Defaults: selectors-4 (selector) :disabled
Abstract: This is a delta specification over CSS-UI Level 3.
Once the level 3 specification is final,
its content will be integrated into this specification,
which will then replace it.
Until then, CSS-UI Level 4 only contains additions and extensions to level 3.
</pre>
<h2 id="intro">Introduction</h2>
Issue: Add final level 3 content
<h2 id="interaction">Module Interactions</h2>
Issue: Add final level 3 content
<h2 id="box-model">Box Model addition</h2>
<h3 id="box-sizing">'box-sizing' property</h3>
Issue: Add final level 3 content
<h2 id="outline-props">Outline properties</h2>
Issue: Add final level 3 content
<h3 id="outline">'outline' property</h3>
Issue: Add final level 3 content
<
8000
/div><h3 id="outline-width">'outline-width' property</h3>
Issue: Add final level 3 content
<h3 id="outline-style">'outline-style' property</h3>
Issue: Add final level 3 content
<h3 id="outline-color">'outline-color' property</h3>
Issue: Add final level 3 content
<h2 id="resizing-and-overflow">Resizing & Overflow</h2>
Issue: Add final level 3 content
<h3 id="resize">'resize' property</h3>
Issue: Add final level 3 content
<h3 id="text-overflow"> Overflow Ellipsis: the 'text-overflow' property</h3>
Issue: Add final level 3 content
<h2 id="pointing-keyboard">Pointing Devices and Keyboards</h2>
<h3 id="pointer-interaction">Pointer interaction</h3>
<h4 id="cursor">'cursor' property</h4>
Issue: Add final level 3 content
Issue: Amend the definition of ''cursor/auto''
to show ''cursor/default'' rather than ''cursor/text''
over text when 'user-select' is ''user-select/none''.
<h3 id="insertion-caret">Insertion caret</h3>
<h4 id="caret-color">Coloring the insertion caret: 'caret-color'</h4>
Issue: Add final level 3 content
Issue: Amend the definition of ''caret-color/auto'' to highlight
the fact that when 'caret-shape' is ''caret-shape/block'',
ensuring good visibility and contrast means not using
currentColor.
<h4 id="caret-blink-time">Blinking speed of the insertion caret: 'caret-blink-time'</h4>
<pre class='propdef'>
Name: caret-blink-time
Value: auto | <<time>>{1,2}
Initial: auto
Applies to: elements that accept input
Inherited: yes
Percentages: N/A
Media: interactive
Computed value: Same as specified value, except if only 1 <<time>> is specified, in which case the computed value has 2 instances of <<time>>, both with the same value as the one which was specified.
Animatable: no
</pre>
On most platforms and in most UAs,
the text insertion caret blinks.
This property allows the author
to control the speed at which it blinks,
or to turn off blinking entirely.
Issue: Do we actually need fine control over the timing,
or would "caret-blink: auto | no-blink" be enough?
When the computed value is ''caret-blink-time/auto'',
the UA determines the speed at which the cursor blinks,
if at all. It should follow platform conventions and settings.
If two <<time>> values are specified,
the caret blinks.
The first value indicates how long the caret stays on,
and the second value how long the caret stays off.
If the second value is ommitted,
it defaults to the same as the first one.
Both values must be zero or more.
Note: See <a href="http://www.w3.org/TR/WCAG20/#seizure">Guideline 2.3: Seizures: Do not design content in a way that is known to cause seizures</a> [[WCAG20]].
If the second value is 0,
or if both values are 0,
the caret does not blink and is always on.
Note: It is recommended to stop the caret from blinking using ''caret-blink-time: 0''
when applying custom animations using [[CSS3-ANIMATIONS]],
to prevent the blinking and the animation to interfere.
If the first value is 0 and the second is not,
the caret is always off,
making it effectively invisible.
<div class=example>
The following rule gives a caret that stays on for 1 second,
and off for half a second.
<pre><code class="lang-css">
input { caret-blink-time: 1s 500ms; }
</code></pre>
</div>
<div class=example>
A user who is disturbed by or has adverse reactions to blinking or flashing visuals
may want to make all carets static and non-blinking,
regardless of platform defaults or author settings.
This can be accomplished by with the folliwing rule in the user stylesheet.
<pre><code class="lang-css">
/* prevent the caret from blinking/flashing */
:read-write { caret-blink-time: 0 !important; }
/* prevent changes of caret-color, including animations */
:read-write { caret-color:auto !important; }
</code></pre>
</div>
UAs that do not have an editable user stylesheet
should provide a setting to disable
<a href="http://www.w3.org/TR/WCAG20/#blinksdef">blinking</a>,
<a href="http://www.w3.org/TR/WCAG20/#flash-def">flashing</a>
and animated carets.
UAs that do have an editable user stylesheet may want to provide this setting as well.<
77F4
/div>
See [[WCAG]] <a href="http://www.w3.org/TR/WCAG20/#time-limits-pause">Guideline 2.2</a>
and <a href="http://www.w3.org/TR/WCAG20/#seizure">Guideline 2.3</a>
for details.
<div class=example>
Normally, the caret blinks between on and off.
This makes it alternate between 2 colors.
<pre><code class="lang-css">
textarea {
caret-blink-time: 0;
caret-color: blue;
animation: caret-alternate 2s step-end infinite;
}
@keyframes caret-alternate {
50% { caret-color: red; }
}
</code></pre>
The simulated rendering below illustrates how this would look.
<style>
@-webkit-keyframes caret-alternate { 50% { border-color: red; } }
@keyframes caret-alternate { 50% { border-color: red; } }
</style>
<div style="border:inset; background: white; width: 10em;">
Text area
with color-alternating caret<span style="border-right: 2px solid blue;animation: caret-alternate 2s step-end infinite;-webkit-animation: caret-alternate 2s step-end infinite;"></span>
</div>
</div>
<h4 id="caret-shape">Shape of the insertion caret: 'caret-shape'</h4>
<pre class='propdef'>
Name: caret-shape
Value: ''auto'' | ''bar'' | ''block'' | ''underscore''
Initial: auto
Applies to: elements that accept input
Inherited: yes
Percentages: N/A
Media: interactive
Computed value: Same as specified value
Animatable: no
</pre>
This property allows authors to specify
the desired shape of the text insertion caret.
Within the context of this definition, <dfn>character</dfn> is
to be understood as <em>extended grapheme cluster</em>,
as defined in [[!UAX29]], and <dfn>visible character</dfn>
means a character with a non-zero advance measure.
<dl dfn-type=value dfn-for=caret-shape>
<dt><dfn>auto</dfn>
<dd>The UA determine the shape of the caret.
It should match platform conventions,
and may be adjusted based on context.
For example, if a UA switches between insert mode and overtype mode when the
user presses the <em>insert</em> key on their keyboard,
it may show a ''caret-shape/bar'' caret in insert mode,
and a ''caret-shape/block'' caret in overtype mode.
<dt><dfn>bar</dfn>
<dd>The UA must render the text insertion caret
as a thin bar placed at the insertion point.
This means it is between, before, or after characters, not over them.
It should be perpendicular to the inline progression direction,
although UAs may render it slanted when inserting italic or oblique text.
<dt><dfn>block</dfn>
<dd>The UA must render the text insertion caret
as a rectangle overlapping the next visible character following the insertion point.
If there is no visible character after the insertion point,
the UA must render the caret after the last visible character.
UAs may render it as a slanted rectangle when inserting italic or oblique text.
<dt><dfn>underscore</dfn>
<dd>The UA must render the text insertion caret
as a thin line <a>under</a> (as defined in [[!CSS-WRITING-MODES-3]]
the next visible character following the insertion point.
If there is no visible character after the insertion point,
the UA must render the caret after the last visible character.
</dl>
The width of the ''caret-shape/block'' and ''caret-shape/underscore'' carets
should be the advance measure of the next visible character after the insertion point,
or ''1ch'' if there is no next visible character
or if this information is impractical to determine.
When determining the orientation and appearance of the caret,
UAs must take into account the <a>writing mode</a> [[!CSS-WRITING-MODES-3]]
and must apply transformations [[!CSS-TRANSFORMS-1]].
If the edited text is laid out out on a path,
for instance by using the SVG <{textPath}> element,
UAs should also account for this.
The stacking position of the caret is left undefined, within the following constraints:
<ul>
<li>The caret must not be obscured by the background of the element
<li>UAs must render ''caret-shape/block'' carets so that the
character it overlaps with is not obscured by the caret
</ul>
<div class=example>
This illustrates the typical appearance of the various caret shapes.
In each of the sample renderings below,
the insertion point is between the letters u and m.
<style>
@-webkit-keyframes caret-bar { 50% { outline-color: transparent; } }
@-webkit-keyframes caret-block { 50% { background: transparent; } }
@-webkit-keyframes caret-underscore { 50% { border-color: transparent; } }
@keyframes caret-bar { 50% { outline-color: transparent; } }
@keyframes caret-block { 50% { background: transparent; } }
@keyframes caret-underscore { 50% { border-color: transparent; } }
#caret-shape-example {
min-width: 25em;
}
#caret-shape-example,
#caret-shape-example td,
#caret-shape-example th {
border: solid 1px;
}
#caret-shape-example td+td {
background:white;
}
</style>
<table id="caret-shape-example">
<tr><th>'caret-shape'<th>Sample rendering
<tr><td>''bar''<td>Lorem ipsu<span style="outline: 1px solid black;animation: caret-bar 2s step-end infinite;-webkit-animation: caret-bar 2s step-end infinite;">​</span>m
<tr><td>''block''<td>Lorem ipsu<span style="background: #bbb; -webkit-animation: caret-block 2s step-end infinite;animation: caret-block 2s step-end infinite;">m</span>
<tr><td>''underscore''<td>Lorem ispu<span style="border-bottom: 2px solid black; -webkit-animation: caret-underscore 2s step-end infinite; animation: caret-underscore 2s step-end infinite;">m</span>
</table>
</div>
<div class=example>
''caret-shape/underscore'' or ''caret-shape/block'' carets are commonly used
in terminals and command lines,
as in this example.
<pre><code class="lang-css">
.console {
caret-shape: underscore;
background: black;
color: white;
font-family: monospace;
padding: 1ex;
}
</code></pre>
<style>
@-webkit-keyframes terminal-caret { 50% { border-color: transparent; } }
@keyframes terminal-caret { 50% { border-color: transparent; } }
</style>
<pre style="background: black; color: white; font-family: monospace; padding: 1ex">
user@host:css-ui-4 $ ls -a
. .. Overview.bs Overview.html
user@host:css-ui-4 $ <span style="border-bottom: 2px solid white;animation: terminal-caret 2s step-end infinite;-webkit-animation: terminal-caret 2s step-end infinite;"> </span>
</pre>
</div>
<h4 id="caret">Insertion caret shorthand: 'caret'</h4>
<pre class='propdef'>
Name: caret
Value: <<'caret-color'>> || <<'caret-blink-time'>> || <<'caret-shape'>>
Initial: auto
Applies to: elements that accept input
Inherited: yes
Percentages: N/A
Media: interactive
Computed value: See individual properties
Animatable: See individual properties
</pre>
This property is a shorthand for setting
'caret-color', 'caret-blink-time' and 'caret-shape' in one declaration.
Omitted values are set to their initial values.
<div class=example>
This example illustrates using the various caret related properties
in combination.
They are used here to simulate the appearance of the caret
on an old phosphor computer monitor.
<pre><code class="lang-css">
#old-screen {
caret: block 0s;
animation: old-caret 2s infinite;
/*styling of the screen omitted for brevity */
}
@keyframes old-caret {
from, 50% { caret-color: green; }
75%, to { caret-color: transparent; }
}
</code></pre>
<style>
#old-screen {
border-radius: 1em;
padding: 1em;
color: green;
font-family: monospace;
background: repeating-linear-gradient(#030 0px, #030 1px, #020 1px, #020 3px);
}
#old-screen span {
display:inline-block;
caret: block 0s;
animation: caret-old 2s infinite;
-webkit-animation: caret-old 2s infinite;
}
@keyframes caret-old {
from, 50% { background-color: green; }
75%, to { background-color: transparent; }
}
@-webkit-keyframes caret-old {
from, 50% { background-color: green; }
75%, to { background-color: transparent; }
}
</style>
<div id="old-screen" style="height: 100px">> <span> </span></div>
</div>
<h3 id="keyboard">Keyboard control</h3>
<h4 id="nav-dir">Directional focus navigation: the 'nav-up', 'nav-right', 'nav-down', 'nav-left' properties</h4>
Issue: Add final level 3 content
<h4 id="input-method-editor">Obsolete: the ime-mode property</h4>
Issue: Add final level 3 content
<h2 id="user-interaction">User Interaction</h2>
<h3 id="content-selection">Controlling content selection</h3>
The 'user-select' property enables authors to specify
which elements in the document can be selected by the user and how.
This allows for easier interactions when not
all elements are equally useful to select,
avoiding accidental selections of neighbouring content.
<pre class='propdef'>
Name: user-select
Value: auto | text | none | element | all
Initial: auto
Inherited: no
Applies to: all elements
Media: interactive
Computed value: See below
</pre>
User Agents must not apply the 'user-select' property to
the ''::first-line'' and ''::first-letter'' pseudo elements.
Issue: Whether 'user-select' should apply to ''::before'' and
''::after'' is an open question.
The computed value is the specified value,
except:
<ol>
<li>on <a>editable element</a>s
where the computed value is always ''user-select/element''
regardless of the specified value
<li>when the specified value is ''user-select/auto'',
which computes one of the other values as defined below
</ol>
For the purpose of this specification,
an <dfn>editable element</dfn> is either
an <a href="https://dvcs.w3.org/hg/editing/raw-file/tip/editing.html#editing-host">editing host</a>
or a <a href="http://www.w3.org/TR/html/forms.html#mutability">mutable</a> form control with textual content,
such as <{textarea}>.
Issue: Should there be constraints
on what happens to the computed value
on elements that are editable descendants of editing hosts?
The semantics are not obvious.
Maybe ''user-select/none'' should compute to ''text'',
or maybe all values should compute to ''text''.
<dl dfn-type=value dfn-for=user-select>
<dt><dfn>auto</dfn>
<dd>The computed value of ''user-select/auto'' is determined as follows:
<ul>
<li>If the element is an <a>editable element</a>,
the computed value is ''element''
<li>Otherwise,
if the computed value of 'user-select' on the parent of this element is ''all'',
the computed value is ''all''
<li>Otherwise,
if the computed value of 'user-select' on the parent of this element is ''user-select/none'',
the computed value is ''user-select/none''
<li>Otherwise, the computed value is ''text''
</ul>
Note: This unusual combination of a non inherited property with an initial value of ''user-select/auto''
whose computed value depends on the parent element
makes it possible to create what is effectively selective inheritance.
This was initially proposed by Microsoft in IE to introduce a behavior similar to inheritance
except that the ''element'' value does not inherit.
<dt><dfn>text</dfn>
<dd>The element imposes no constraint on the selection.
<dt><dfn>none</dfn>
<dd>
The UA must not allow selections to be started in this element.
A selection started outside of this element must not end in this element.
If the user attempts to create such a selection,
the UA must instead end the selection range at the element boundary.
Note: As of the time of writing, experimental implementations do not all behave like this.
Firefox does.
Chrome and Safari almost do: for a selection started after the element
and trying to go backwards into the element
they behave as specified here,
but for a selection started before the element
and trying to go into the element
they behave as if the element has ''all'' and select it entirely.
IE does not restrict selections started outside of the element
from going into it at all.
Another difference is that in Chrome and Safari,
if the user attempts to start a selection inside a ''user-select: none'',
and to end the selection out of it,
a selection will be created from the boundary of the element
to the user-designated end-point.
Firefox and Internet explorer behave as prescribed in this specification
and do not create a selection at all.
However, if this element has descendants on which the computed value of 'user-select' is not ''user-select/none'',
selections that start and end within these descendants are allowed.
The UA must allow selections to extend across this element,
and must exclude this element from such a selection.
An exception is made for UAs which do not support multiple ranges per selection,
and they may include this element.
If the element has descendants on which 'user-select' does not compute to ''user-select/none'',
these descendants must be included in a selection extending across the element.
Note: ''user-select: none'' on a non-editable descendant of an editable element
means that in addition to not being editable,
that descendant is also not deletable,
neither directly nor by attempting to include it in a broader selection
and then deleting that selection.
This matters for example in template-based editing,
where an editable template may contain sections which must be preserved.
As 'user-select' is a UI convenience mechanism,
not a copy protection mechanism,
the UA may provide an alternative way for the user
to explicitly select the text even when 'user-select' is ''user-select/none''.
Note: ''user-select/none'' is not a copy protection mechanism,
and using it as such is ineffective:
User Agents are allowed to provide ways to bypass it,
it will have no effect on legacy User Agents that do not support it,
and the user can disable it through the user style sheet or equivalent mechanisms
on UAs that do anyway.
Instead, ''user-select/none'' is meant to
make it easier for the user to select the content they want,
by letting the author disable selection on UI elements
that are not useful to select.
Tools such as CSS validators, linters or in-browser developer tools
are encouraged to use heuristics
to detect and warn against incorrect or abusive usage
that would hamper usability
or violate common user expectations.
<dt><dfn>element</dfn>
<dd>UAs must not allow a selection which is started in this element
to be extended outside of this element.
A selection started outside of this element must not end in this element.
If the user attempts to create such a selection,
the UA must instead end the selection range at the element boundary.
The UA must allow selections to extend across this element,
and such selections must include the content of the element.
Note: At the time of writing, experimental implementations behave differently from eachother
about selections started outside and selections going into the element.
The behavior can be observed even on browsers that do not explicitly support ''element''
by trying to select into a <{textarea}> or a contenteditable element.
Issue: Not sure the name ''user-select:element'' is particularly clear
about what this means.
How about something like "contain" or "inside" instead?
<dt><dfn>all</dfn>
<dd>The content of the element must be selected atomically:
If a selection would contain part of the element,
then the selection must contain the entire element including all its descendants.
If the element is selected
and the computed value of 'user-select' on its parent is ''all'',
then the parent must be included in the selection, recursively.
If this element has descendants on which the computed value of 'user-select' is not ''all''
and if a selection is entirely contained in these descendants,
then the selection is not extended to include this whole element.
</dl>
Note: Selections can include more than just text and extend over images, tables, videos, etc.
The behavior when copying and pasting a such selections is out of scope for this specification.
The following additions are made to the UA stylesheet for HTML:
<pre><code class="lang-css">
button, meter, progress, select { user-select: none; }
</code></pre>
Issue: the list above is incomplete, and needs to include
at least the various button-like variants of <{input}>.
<h2 id="form-styling">Form Control Styling</h2>
<h3 id="appearance-switching">Switching appearance</h3>
While the way most elements in a document look can be fully controlled by CSS,
form controls are typically rendered by UAs using native UI controls of the host operating system,
which can neither be replicated nor styled using CSS.
This specification introduces the 'appearance' property
to provide some control over this behavior.
In particular, using ''appearance: none'' allows authors
to suppress the native style of form controls,
so that CSS can be used to fully restyle them.
<pre class="propdef">
Name: appearance
Value: ''auto'' | ''none'' | ''button''
Initial: auto
Applies To: all elements
Inherited: no
Computed value: As specified
Media: all
</pre>
Issue: Should ''appearance/auto'' compute to ''appearance/none'' on regular elements?
I would say no:
to be consistent, we should then have ''appearance/auto'' compute to ''button'' on buttons, etc.
If we did that,
every time we introduced a new value,
we would change what ''appearance/auto'' computes to on some elements,
which doesn't sounds desirable.
Note: This specification intentionally refrains from making the appearance
of all possible form controls and sub-controls available as values,
as had previously been attempted by earlier proposals for this property
and by several UA vendors in experimental implementations.
Experience has shown that such a list would be very long and not practical to maintain,
and UAs would need to add non-standard values
to account for the behavior of non-standard pseudo-elements
sometimes used to implement form controls.
Moreover, many values of such an enumeration only make sense
on a single element or pseudo-element,
and are never used outside of the UA stylesheet.
Instead, this specification will only provide
''appearance/auto'', ''appearance/none'', and
values which are useful in an author or user stylesheet
and for which interoperability can be achieved.
UAs cannot therefore use the 'appearance' property
in the UA stylesheet to give each control is native look and feel,
and must use ''appearance:auto'' instead.
Issue: IE supports -webkit-appearance, and also includes the textfield value.
Presumably this was done due to compatibility problems,
so we may want to include it as well.
<dl dfn-type=value dfn-for=appearance>
<dt><dfn>auto</dfn>
<dd>UAs may render form controls using native controls of the host operating system
or with a look and feel not otherwise expressible in CSS.
Elements other than form controls must be rendered as if ''appearance/none'' had been specified.
<dt><dfn>none</dfn>
<dd> The element is rendered following the usual rules of CSS.
Replaced elements other than form controls are not affected by this,
and remain replaced elements.
From controls are <em>not</em> made to look like native controls of the host operating system.
See below for details.
Issue: Shouldn't this be called "normal" instead?
''appearance/none'' makes it sound like the targeted element will disappear.
<dt><dfn>button</dfn>
<dd>The element is rendered with the look and feel of a push button,
similar to the rendering of the HTML <{button}> element.
Issue: There are strong concerns as to whether this property should have any value
other than ''appearance/auto'' and ''appearance/none''.
The ''appearance/button'' value may be necessary due to backward compatibility concerns,
but if it is not, there is a strong possibility that it will be dropped.
</dl>
On form control elements where the computed value is ''appearance/auto''
and on other elements where the computed value is neither ''appearance/auto'' nor ''appearance/none'',
UAs may disregard some CSS properties
to ensure that the intended appearance is preserved,
or because these property may not be meaningful for the chosen appearance.
However, the following properties must not be disregarded:
<ul>
<li>'appearance'
<li>'display'
<li>'visibility'
<li>'position'
<li>'top'
<li>'right'
<li>'bottom'
<li>'left'
<li>'float'
<li>'clear'
</ul>
Issue: Are there more properties should include in this list?
Should we remove some?
Should whitelist the properties that are ok to ignore instead of
blacklisting those that are not?
Either way, UAs do ignore some properties when rendering form controls,
so this specification needs to say something about this.
All decorative visual aspects of a form control which are not caused by a CSS style rule
must be suppressed when the appearance is changed using 'appearance',
even if the UA's internal representation for this element
was composed of multiple elements or pseudo elements combined together.
For example, <{select}> is often rendered with an arrow on the right si
973A
de
indicating that the list will be expanded if the element is clicked,
If the computed value of 'appearance' is ''appearance/none'', this
must disappear.
However, the UA must preserve aspects of the form control
which are necessary to operate the control with its original semantics.
This does not include aspects of a control which are merely needed to observe the state the control is in,
only those that are needed for the user to be able to modify the state of the control.
The UA may however give them a different look and feel
as long as it remains possible to operate the control.
For example,
the slider of an <code class="lang-markup"><input type=range></code> is preserved
(or replaced by an equivalent mechanism)
even if 'appearance' is ''appearance/none''
as it would otherwise not be possible to change the value of the range with the mouse or touchscreen.
On the other hand,
the check mark in an <code class="lang-markup"><input type=checkbox checked></code>
must be suppressed,
as it merely indicates the state the element is in,
which can be styled in different ways using the '':checked'' selector.
Issue: UAs are inconsistent about the preceding two paragraphs.
What is specified here attempts to give some logic
to what is preserved and what is not,
based on the use-cases for 'appearance'.
UAs should include in their User Agent stylesheet style rules
to give form controls a recognizable shape when 'appearance' is ''appearance/none''.
Note: Authors may therefore need to override these UA style rules to get the styling
they intended, possibly by using ''all: unset''.
Issue: This usage of the 'all' property would remove focus indicators
created by the 'outline' property,
which seems undesirable.
Using ''all: default'' would not solve it, as it would fail to remove
the UA styles as intended.
How can we mitigate this?
The behavior and semantics of elements remain defined by the host language,
and are not influenced by this property.
For example, regardless of the computed value of 'appearance':
<ul>
<li>Elements which can be in different states keep this ability,
and the relevant pseudo-classes match as usual.
<li>If a <{select}> element is activated,
the UI to choose one of the associated <{option}> elements is shown
(although it may look different).
<li>Event handlers attached to the element trigger as usual.
</ul>
Conversely, changing the appearance of an element must not cause it
to acquire the semantics, pseudo classes, event handlers, etc
that are typical of the element whose appearance it acquires.
For example, neither '':enabled'' nor '':disabled'' match on
a <{div}> styled with ''appearance: button''.
The ability for an element to be focused
is also not changed by the 'appearance' property.
<div class=example>
An author wanting to customize the look and feel of check boxes in HTML could use the following:
<pre><code class="lang-css">
input[type=checkbox] {
appearance: none;
all: unset;
width: 1em;
height: 1em;
display: inline-block;
background: red;
}
input[type=checkbox]:checked {
border-radius: 50%;
background: green;
}
</code></pre>
<code class="lang-markup"><input type="checkbox"></code> would be rendered as
<span style="display: inline-block; width: 1em; height: 1em; background: red;"></span>,
while <code class="lang-markup"><input type="checkbox" checked></code> would be rendered as
<span style="display: inline-block; width: 1em; height: 1em; background: green; border-radius: 50%;"></span>,
and activating (for example by clicking) the element would toggle the state as usual.
</div>
<hr title="Separator from footer">
<h2 class="no-num" id="acknowledgments">Appendix A. Acknowledgments</h2>
This appendix is <em>informative</em>.
Issue: Add final level 3 content
<h2 class="no-num" id="changes">Appendix B. Changes</h2>
This appendix is <em>informative</em>.
Issue: List changes sinces Level 3
<h2 class="no-num" id="default-style-sheet">Appendix C. Default style sheet additions for HTML</h2>
Issue: Add final level 3 content
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