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Text spacing rewrite (#1923)
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* Add new letter-spacing rule and deprecate old one

* Add new word-spacing rule and deprecate old one

* Clean up assumptions

* Clean up

* Clean up

* Add new line-height rule and deprecate old one

* Replace old letter spacing version rather than deprecating it

* Replace old line height version rather than deprecating it

* Replace old word spacing version rather than deprecating it

* Target text nodes

* Improve background note

* Apply suggestion from review

* Clean up

* Target text nodes rather than their parents

* Target text nodes rather than their parents

* Add missing reference

* Update example

* Apply to parent of text nodes, not text nodes

* Apply suggestions from code review

Co-authored-by: Carlos Duarte <[email protected]>

* Typos

Co-authored-by: Carlos Duarte <[email protected]>

* Typos

---------

Co-authored-by: Carlos Duarte <[email protected]>
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Jym77 and Carlos Duarte committed Oct 13, 2023
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168 changes: 104 additions & 64 deletions ...es/letter-spacing-not-important-24afc2.md → ...tant-letter-spacing-wide-enough-24afc2.md
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---
id: 24afc2
name: Letter spacing in style attributes is not !important
name: Important letter spacing in style attributes is wide enough
rule_type: atomic
description: |
This rule checks that the `style` attribute is not used to prevent adjusting `letter-spacing` by using `!important`, except if it's at least 0.12 times the font size.
Expand All @@ -16,74 +16,72 @@ input_aspects:
acknowledgments:
authors:
- Jean-Yves Moyen
previous_authors:
- Jey Nandakumar
funding:
- WAI-Tools
---

## Applicability

This rule applies to any [HTML element][] that is [visible][] and for which the `style` attribute [declares][declared] the [letter-spacing][] CSS property.
This rule applies to any [HTML element][] with one or more [visible][] [text node][] children, when all the following are true for the `letter-spacing` property of the element:

## Expectation
- the [specified][] value is [declared][] in a `style` attribute; and
- the [computed][] value is [important][].

For each test target, at least one of the following is true:
## Expectation

- **not important**: the [computed][] value of its [letter-spacing][] property is not [important][]; or
- **wide enough**: the [computed][] value of its [letter-spacing][] property is at least 0.12 times the [computed][] value of its [font-size][] property; or
- **cascade**: the [cascaded][] value of its [letter-spacing][] property is not a value [declared][] in its `style` attribute.
For each test target, the [computed][] value of its `letter-spacing` property is at least 0.12 times the [computed][] value of its `font-size` property.

## Assumptions

- There is no mechanism available on the page to adjust [letter-spacing][]. If there is such a mechanism, it is possible to fail this rule while [Success Criterion 1.4.12 Text Spacing][sc1412] is still satisfied.
- There is no mechanism available on the page to adjust `letter-spacing`. If there is such a mechanism, it is possible to fail this rule while [Success Criterion 1.4.12 Text Spacing][sc1412] is still satisfied.

- The font size is constant for all text in the element. If `font-size` changes (e.g., through use of the `::first-line` pseudo-element) then the required letter spacing would also change throughout the element. This is untested by the current rule.

- This rule assumes that WCAG's meaning for the "Letter spacing style property" is the value of the CSS `letter-spacing` property rather than the actual space between letters. The value of the CSS property is _added_ to whichever spacing already exist (for example, due to kerning). Thus, the actual space between letters can be larger than the value of the `letter-spacing` property. If [Success Criterion 1.4.12 Text Spacing][sc1412] is concerned by the actual space between letters, then this rule may fail (with the `letter-spacing` property being too small) while the Success Criterion is still satisfied (with the actual space being enough).

- This rule assumes that when inter-letters space is changed because of justification, the `letter-spacing` property is not changed. Therefore, whether a text is justified or not doesn't change the result of this rule. Note that justifying text is a failure of [Success Criterion 1.4.8 Visual Presentation][sc148].

- The target text node expresses something in a human language written in a script that uses the `letter-spacing` property.

## Accessibility Support

While some assistive technologies are able to set [user origin][] or [user agent origin][] styles, others, such as browser extensions, are only able to set styles with the [author origin][]. Such assistive technologies cannot create styles "winning" the [cascade sort][] over a `style` attribute with an [important][] declaration.

## Background

When a style is [declared][] in the `style` attribute with an [important][] declaration, it "wins" the [cascade sort] over any other style from [author origin][], i.e. it cannot be overridden by any of these. On the other hand, if such a style is [declared][] in a style sheet, it can still "lose" the [cascade sort][] to declarations with higher [specificity][] or simply coming from a later style sheet (such as ones injected by assistive technologies). This rule ensures that the element is not in the first case and that the style can be overridden by users, unless it is already at least the minimum required threshold. [Important][] styles that are declared with the [user][user origin] or [user agent][user agent origin] origin can win the [cascade sort][] over styles with the [author origin][].
Styles [declared][] in a `style` attribute have higher [cascade specificity][] than any selector; therefore, they "win" the [cascade sort] over any other style from [author origin][], i.e. it cannot be overridden by any of these. On the other hand, if such a style is [declared][] in a style sheet, it can still "lose" the [cascade sort][] to declarations with higher [specificity][] or simply coming from a later style sheet (such as ones injected by assistive technologies). This rule ensures that the element is not in the first case and that the style can be overridden by users, unless it is already at least the minimum required threshold. [Important][] styles that are declared with the [user][user origin] or [user agent][user agent origin] can win the [cascade sort][] over styles with the [author origin][].

CSS specifications define each declaration as being either [important][] (if it has the `!important` annotation) or [normal][]. Given that `normal` is also a keyword for this property, and that `!important` is wider known that this distinction, this rule rather uses "[important][]"/"not [important][]" to avoid confusion.
CSS specifications define each declaration as being either [important][] (if it has the `!important` annotation) or [normal][]. Given that `normal` is also a keyword for some properties, and that `!important` is wider known than this distinction, this rule rather uses "[important][]"/"not [important][]" to avoid confusion.

### Bibliography

- [Understanding Success Criterion 1.4.12: Text Spacing](https://www.w3.org/WAI/WCAG21/Understanding/text-spacing.html)
- [CSS Text Module Level 3 - Spacing](https://www.w3.org/TR/css-text-3/#spacing)
- [CSS Visual formatting model details](https://drafts.csswg.org/css2/visudet.html)

### About test cases

Test cases descriptions abusively refer to the CSS properties of text nodes, meaning the one of their parent.

## Test Cases

### Passed

#### Passed Example 1

This `p` element has a **not [important][]** [computed][] `letter-spacing`.

```html
<p style="letter-spacing: 0.1em">
The toy brought back fond memories of being lost in the rain forest.
</p>
```

#### Passed Example 2

This `p` element has a [computed][] `letter-spacing` of 0.15 time the font size, which is **wide enough**.
This `p` element has a [computed][] `letter-spacing` of 0.15 time the `font-size`.

```html
<p style="letter-spacing: 0.15em !important">
The toy brought back fond memories of being lost in the rain forest.
</p>
```

#### Passed Example 3
#### Passed Example 2

This `p` element has a [computed][] [letter-spacing][] of `3px`, which is **wide enough** (the threshold is `3px`).
This `p` element has a [computed][] `letter-spacing` of `3px`, which is exactly 0.12 the `font-size` of `25px`.

```html
<style>
Expand All @@ -97,64 +95,48 @@ This `p` element has a [computed][] [letter-spacing][] of `3px`, which is **wide
</p>
```

#### Passed Example 4
#### Passed Example 3

This `p` element has two [declared][] values for its `letter-spacing` property. The latest wins the [cascade sort][]. It has a value of `0.15em`, and is **wide enough**.
This `p` element has two [declared][] values for its `letter-spacing` property. The latest wins the [cascade sort][]. It has a value of `0.15em`, which is wide enough.

```html
<p style="letter-spacing: 0.1em !important; letter-spacing: 0.15em !important">
The toy brought back fond memories of being lost in the rain forest.
</p>
```

#### Passed Example 5
#### Passed Example 4

This `p` element has two [declared][] values for its `letter-spacing` property. The one which is [important][] wins the [cascade sort][]. It has a value of `0.15em`, and is **wide enough**.
This `p` element has two [declared][] values for its `letter-spacing` property. The one which is [important][] wins the [cascade sort][]. It has a value of `0.15em`, which is wide enough.

```html
<p style="letter-spacing: 0.15em !important; letter-spacing: 0.1em">
The toy brought back fond memories of being lost in the rain forest.
</p>
```

#### Passed Example 6

The [cascaded][] value of the `letter-spacing` property of this `p` element is [declared][] in the style sheet, not in the `style` attribute (it wins the [cascade sort][] because it is [important][]). Thus, the `p` element matches the **cascade** condition.

```html
<style>
p {
letter-spacing: 0.1em !important;
}
</style>

<p style="letter-spacing: 0.15em">
The toy brought back fond memories of being lost in the rain forest.
</p>
```

#### Passed Example 7
#### Passed Example 5

The [computed][] value of the `letter-spacing` property of this `p` element is **not [important][]**. The [computed][] value of the `letter-spacing` property of this `span` element is the [inherited][] value, that is the [computed][] value of its parent and therefore also **not [important][]**.
This `p` element has a [computed][] `letter-spacing` of `2px`, 0.2 times its [computed][] `font-size` of `10px`; the `div` element has no [visible][] text node children.

```html
<p style="letter-spacing: 0.1em">
<span style="letter-spacing: inherit !important;">
<div style="font-size: 16px; letter-spacing: 2px !important">
<p style="font-size: 10px;">
The toy brought back fond memories of being lost in the rain forest.
</span>
</p>
</p>
</div>
```

#### Passed Example 8
#### Passed Example 6

The [computed][] value of the `letter-spacing` property of this `p` element is **not [important][]**. The [computed][] value of the `letter-spacing` property of this `span` element is the [inherited][] value, that is the [computed][] value of its parent and therefore also **not [important][]**.
This `p` element has a [computed][] `letter-spacing` of 0.2 times its `font-size`; the `div` element has no [visible][] text node children.

```html
<p style="letter-spacing: 0.1em">
<span style="letter-spacing: unset !important;">
<div style="letter-spacing: 0.1em !important">
<p style="letter-spacing: 0.2em !important;">
The toy brought back fond memories of being lost in the rain forest.
</span>
</p>
</p>
</div>
```

### Failed
Expand Down Expand Up @@ -219,48 +201,106 @@ There is no HTML element.

#### Inapplicable Example 2

This `p` element is not [visible][] because of `display: none`.
There is no text node.

```html
<div style="letter-spacing: 0.1em !important;"></div>
```

#### Inapplicable Example 3

There is no [visible][] text node because of `display: none`.

```html
<p style="display: none; letter-spacing: 0.1em !important;">
The toy brought back fond memories of being lost in the rain forest.
</p>
```

#### Inapplicable Example 3
#### Inapplicable Example 4

This `p` element is not [visible][] because it is positioned off-screen.
There is no [visible][] text node because it is positioned off-screen.

```html
<p style="position: absolute; top: -999em; letter-spacing: 0.1em !important;">
The toy brought back fond memories of being lost in the rain forest.
</p>
```

#### Inapplicable Example 4
#### Inapplicable Example 5

The `style` attribute of this `p` element does not [declare][declared] the `letter-spacing` property.
This `p` element's `letter-spacing` property is not [declared][] in a `style` attribute.

```html
<p style="width: 60%">
The toy brought back fond memories of being lost in the rain forest.
</p>
```

#### Inapplicable Example 6

The [specified][] value of the `letter-spacing` property of this `p` element is [declared][] in the style sheet, not in the `style` attribute (it wins the [cascade sort][] because it is [important][]).

```html
<style>
p {
letter-spacing: 0.1em !important;
}
</style>

<p style="letter-spacing: 0.15em">
The toy brought back fond memories of being lost in the rain forest.
</p>
```

#### Inapplicable Example 7

This `p` element does not have an [important][] [computed][] `letter-spacing`.

```html
<p style="letter-spacing: 0.1em">
The toy brought back fond memories of being lost in the rain forest.
</p>
```

#### Inapplicable Example 8

The [computed][] value of the `letter-spacing` property of this `span` element is the [inherited][] value, that is the [computed][] value of the `p` element and therefore not [important][]; the `p` element has no [visible][] text node children.

```html
<p style="letter-spacing: 0.1em">
<span style="letter-spacing: inherit !important;">
The toy brought back fond memories of being lost in the rain forest.
</span>
</p>
```

#### Inapplicable Example 9

The [computed][] value of the `letter-spacing` property of this `span` element is the [inherited][] value, that is the [computed][] value of the `p` element and therefore not [important][]; the `p` element has no [visible][] text node children.

```html
<p style="letter-spacing: 0.1em">
<span style="letter-spacing: unset !important;">
The toy brought back fond memories of being lost in the rain forest.
</span>
</p>
```

[author origin]: https://www.w3.org/TR/css-cascade-4/#cascade-origin-author 'CSS Cascading and Inheritance Level 4 (Working draft) - Cascading Origins - Author Origin'
[cascade sort]: https://www.w3.org/TR/css-cascade-4/#cascade-sort 'CSS Cascading and Inheritance Level 4 (Working draft) - Cascade Sort'
[cascaded]: https://www.w3.org/TR/css-cascade-4/#cascaded 'CSS Cascading and Inheritance Level 4 (Working draft) - Cascaded Values'
[cascade specificity]: https://www.w3.org/TR/css-cascade-3/#cascade-specificity 'CSS Cascading and Inheritance Level 4 (Candidate Recommendation) - Cascade specificity'
[computed]: https://www.w3.org/TR/css-cascade-4/#computed 'CSS Cascading and Inheritance Level 4 (Working draft) - Computed Values'
[declared]: https://www.w3.org/TR/css-cascade-4/#declared 'CSS Cascading and Inheritance Level 4 (Working draft) - Declared Values'
[font-size]: https://www.w3.org/TR/css-fonts-4/#propdef-font-size 'CSS Fonts Module Level 4 (Working draft) - Font size: the font-size property'
[html element]: #namespaced-element
[important]: https://www.w3.org/TR/css-cascade-4/#importance 'CSS Cascading and Inheritance Level 4 (Working draft) - Importance'
[inherited]: https://www.w3.org/TR/css-cascade-4/#inheriting 'CSS Cascading and Inheritance Level 4 (Working draft) - Inherited Values'
[letter-spacing]: https://www.w3.org/TR/css-text-3/#propdef-letter-spacing 'CSS Text Module Level 3 - Tracking: the letter-spacing property'
[normal]: https://www.w3.org/TR/css-cascade-4/#normal 'CSS Cascading and Inheritance Level 4 (Working draft) - Normal declarations'
[sc1412]: https://www.w3.org/TR/WCAG21/#text-spacing 'Success Criterion 1.4.12 Text Spacing'
[sc148]: https://www.w3.org/TR/WCAG21/#visual-presentation 'Success Criterion 1.4.8 Visual Presentation'
[specified]: https://www.w3.org/TR/css-cascade-4/#specified 'CSS Cascading and Inheritance Level 4 (Working draft) - Specified Values'
[specificity]: https://www.w3.org/TR/selectors/#specificity 'CSS Selectors Level 4 (Working draft) - Specificity'
[text node]: https://dom.spec.whatwg.org/#text
[user origin]: https://www.w3.org/TR/css-cascade-4/#cascade-origin-user 'CSS Cascading and Inheritance Level 4 (Working draft) - Cascading Origins - User Origin'
[user agent origin]: https://www.w3.org/TR/css-cascade-4/#cascade-origin-ua 'CSS Cascading and Inheritance Level 4 (Working draft) - Cascading Origins - User Agent Origin'
[visible]: #visible 'Definition of visible'
[html element]: #namespaced-element
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