CSS Basic User Interface Module Level 4

ED: http://dev.w3.org/csswg/css-ui-4/
Status Text: This specification will include and extend CSS Basic User Interface Module Level 3. [[CSS3-UI]]
TR: http://www.w3.org/TR/css-ui-4/
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 specification describes user interface related
          properties and values to style HTML and XML (including XHTML).
          It includes and extends user interface related features
          from the properties and values of previous CSS levels.
          It uses various properties and values
          to style basic user interface elements in a document.

Introduction

Purpose

• Extend the user interface features in CSS2.1 and [[CSS3-UI]]
• Provide additional CSS mechanisms to augment or replace other dynamic presentation related features in HTML.
• Introduce directional navigation properties to assist in the construction of user interfaces which make use of a directional navigation model.

Module Interactions

• Section 18.1, section 18.4, and Information on the stacking of outlines defined in Appendix E of Cascading Style Sheets, level 2, revision 1 [[CSS21]]
• User Interface for CSS3 (16 February 2000) [[CSSUI]]

Box Model addition

'box-sizing' property

Outline properties

'outline' property

'outline-width' property

'outline-style' property

'outline-color' property

Resizing & Overflow

'resize' property

Overflow Ellipsis: the 'text-overflow' property

    Name: text-overflow
    New values: ''fade'' | <>
    Computed value: As specified, with <> converted to absolute units
    

fade( <> | <> )

Clip inline content that overflows its line box. Characters may be only partially rendered. In addition, the UA must apply a fade out effect near the edge of the line box, reaching complete transparency at the edge. Issue: Do we need to define the way the fade out is calculated so that the fading is identical across browsers? It should probably be something like ''mask-image: linear-gradient(to right, rgba(0,0,0,1), rgba(0,0,0,0))'', except applied to the relevant portion of the line only. The argument determines the distance over which the fade effect is applied. The <> is resolved against the width of the line box. Values lower than 0 are clipped to 0. Values greater than the width of the line box are clipped to the width of the line box. Issue: If the line box is too short to display the fade effect at the desired length, should we drop the effect, or shrink the distance it is applied over until it fits, or clip the end of the fade?

fade

Same as ''fade()'', but the distance over which the fading effect is applied is determined by the UA. ''1em'' is suggested as a reasonable value.

<div style="text-overflow:fade; overflow:hidden">
CSS IS AWESOME, YES
</div>

Pointing Devices and Keyboards

Pointer interaction

'cursor' property

Insertion caret

Coloring the insertion caret: 'caret-color'

Animation of the insertion caret: 'caret-animation'

Name: caret-animation
Value: auto | blink | none | fade
Initial: auto
Applies to: elements that accept input
Inherited: yes
Percentages: N/A
Media: interactive
Computed value: Same as specified value.
Animatable: no

auto

The UA determines how the caret should be animated, if at all. It should match platform conventions, and may be adjusted based on context. Note: This is typically rendered as a blinking caret.

blink

The UA must display a blinking caret. For accessibility reasons, and based on user preferences, The UA may display a non animated caret instead.

none

The UA must not animate the caret. Note: This is only about UA driven animations of the caret. If CSS animations are used to animate the caret color, these should still apply normally.

fade

The UA must display a caret repeatedly fading in and out, similarly to ''caret-animation/blink'' except it appears and disappears progressively rather than suddenly. For accessibility reasons, and based on user preferences, The UA may display a non animated caret instead.

/* prevent the caret from blinking/flashing */
:read-write { caret-animation: none !important; }

/* prevent changes of caret-color, including animations */
:read-write { caret-color:auto !important; }
	

Shape of the insertion caret: 'caret-shape'

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

auto

The UA determines 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 insert key on their keyboard, it may show a ''caret-shape/bar'' caret in insert mode, and a ''caret-shape/block'' caret in overtype mode.

bar

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.

block

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.

underscore

The UA must render the text insertion caret as a thin line under (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.

• The caret must not be obscured by the background of the element
• UAs must render ''caret-shape/block'' carets so that the character it overlaps with is not obscured by the caret

Insertion caret shorthand: 'caret'

Name: caret
Value: <<'caret-color'>> || <<'caret-animation'>> || <<'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

Keyboard control

Directional focus navigation: the 'nav-up', 'nav-right', 'nav-down', 'nav-left' properties

Obsolete: the ime-mode property

User Interaction

Controlling content selection

		Name: user-select
		Value: auto | text | none | contain | all
		Initial: auto
		Inherited: no
		Applies to: all elements
		Media: interactive
		Computed value: See below
	

1. on editable elements where the computed value is always ''user-select/contain'' regardless of the specified value
2. when the specified value is ''user-select/auto'', which computes one of the other values as defined below

auto

The computed value of ''user-select/auto'' is determined as follows:

• If the element is an editable element, the computed value is ''contain''
• Otherwise, if the computed value of 'user-select' on the parent of this element is ''all'', the computed value is ''all''
• 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''
• Otherwise, the computed value is ''text''

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 ''contain'' value does not inherit.

text

The element imposes no constraint on the selection.

none

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. 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.

contain

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 ''contain'' by trying to select into a <{textarea}> or a contenteditable element. Note: This was initially introduced as an experimental feature in Internet Explorer, under the name user-select: element.

all

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.

	button, meter, progress, select { user-select: none; }
	

Form Control Styling

Switching appearance

Name: appearance
Value: ''auto'' | ''none''
Initial: auto
Applies To: all elements
Inherited: no
Computed value: As specified
Media: all

auto

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.

none

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 not 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.

• 'appearance'
• 'display'
• 'visibility'
• 'position'
• 'top'
• 'right'
• 'bottom'
• 'left'
• 'float'
• 'clear'

• Elements which can be in different states keep this ability, and the relevant pseudo-classes match as usual.
• If a <{select}> element is activated, the UI to choose one of the associated <{option}> elements is shown (although it may look different).
• Event handlers attached to the element trigger as usual.

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;
}
	

Appendix A. Acknowledgments

Appendix B. Changes

• The 'user-select' property has been added
• The 'appearance' property has been added
• The ''text-overflow/fade'' and ''fade()'' values have been added to 'text-overflow'
• The 'caret' shorthand property and the 'caret-shape' and 'caret-animation' properties have been added.

Appendix C. Considerations for Security and Privacy

1. Does this specification deal with personally-identifiable information?

   No.

2. Does this specification deal with high-value data?

   No.

3. Does this specification introduce new state for an origin that persists across browsing sessions?

   No.

4. Does this specification expose persistent, cross-origin state to the web?

   No.

5. Does this specification expose any other data to an origin that it doesn’t currently have access to?

   No.

6. Does this specification enable new script execution/loading mechanisms?

   No.

7. Does this specification allow an origin access to a user’s location?

   No.

8. Does this specification allow an origin access to sensors on a user’s device?

   Yes. The directional focus navigation properties indirectly allow access to the device's keyboard navigation input mechanism such as arrow keys.

9. Does this specification allow an origin access to aspects of a user’s local computing environment?

   No.

10. Does this specification allow an origin access to other devices?

    No.

11. Does this specification allow an origin some measure of control over a user agent’s native UI?

    Yes. The 'cursor' and 'caret-*' properties enable the page to change the display of the cursor and text insertion caret of the user agent’s native UI. In addition the 'outline-style' property’s ''outline-style/auto'' value (and thus 'outline' shorthand) enable the page to potentially display a native focused element outline presentation around any element.

    The 'appearance' property also allows author to turn off native styling and replace it with css based styling.

12. Does this specification expose temporary identifiers to the web?

    No.

13. Does this specification distinguish between behavior in first-party and third-party contexts?

    No.

14. How should this specification work in the context of a user agent’s "incognito" mode?

    No differently.

15. Does this specification persist data to a user’s local device?

    No.

16. Does this specification have a "Security Considerations" and "Privacy Considerations" section?

    Yes.

17. Does this specification allow downgrading default security characteristics?

    No.

Appendix D. Default style sheet additions for HTML