Text spacing rewrite

__tests__/spelling-ignore.yml

@@ -255,6 +255,8 @@
 - 2px
 - 3px
 - 4px
+- 10px
+- 15px
 - 16px
 - 20px
 - 24px

_rules/important-letter-spacing-wide-enough-fsy8c7.md

@@ -0,0 +1,301 @@
+---
+id: fsy8c7
+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.
+accessibility_requirements:
+  wcag21:1.4.12: # Text Spacing (AA)
+    forConformance: true
+    failed: not satisfied
+    passed: further testing needed
+    inapplicable: further testing needed
+input_aspects:
+  - DOM Tree
+  - CSS Styling
+acknowledgments:
+  authors:
+    - Jean-Yves Moyen
+---
+
+## Applicability
+
+This rule applies to any [HTML element][] for which all the following are true:
+
+- the element is has at least one [visible][] text node children; and
+- the [specified][] `letter-spacing` property of the element is [declared][] in a `style` attribute; and
+- the [computed][] `letter-spacing` property is [important][].
+
+The [specified][] `letter-spacing` of the element may be inherited from an ancestor, therefore the test targets do not necessarily have a `style` attribute.
+
+## Expectation
+
+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.
+
+- 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].
+
+- At least one text node child of the element express something in a human language written in a script that 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][].
+
+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.
+
+### 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)
+
+## Test Cases
+
+### Passed
+
+#### Passed Example 1
+
+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 2
+
+This `p` element has a [computed][] `letter-spacing` of `3px`, which is exactly 0.12 the `font-size` of `25px`.
+
+```html
+<style>
+	p {
+		font-size: 25px;
+	}
+</style>
+
+<p style="letter-spacing: 3px !important">
+	The toy brought back fond memories of being lost in the rain forest.
+</p>
+```
+
+#### 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`, 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 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`, 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 5
+
+The `div` element has no text node child. The [computed][] `letter-spacing` of the `p` element is `2px`, 0.2 times its [computed][] `font-size` of `10px`
+
+```html
+<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.
+	</p>
+</div>
+```
+
+#### Passed Example 6
+
+The `div` element has no text node child. The [computed][] `letter-spacing` of the `p` element is 0.2 times its `font-size`.
+
+```html
+<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.
+	</p>
+</div>
+```
+
+### Failed
+
+#### Failed Example 1
+
+This `p` element has a [computed][] `letter-spacing` of only 0.1 times the font size, which is below the required minimum.
+
+```html
+<p style="letter-spacing: 0.1em !important">
+	The toy brought back fond memories of being lost in the rain forest.
+</p>
+```
+
+#### Failed Example 2
+
+This `p` element has a [computed][] `letter-spacing` of `2px` which is only 0.1 times the font size (`20px`), thus below the required minimum.
+
+```html
+<style>
+	p {
+		font-size: 20px;
+	}
+</style>
+
+<p style="letter-spacing: 2px !important">
+	The toy brought back fond memories of being lost in the rain forest.
+</p>
+```
+
+#### Failed Example 3
+
+This `p` element has a [computed][] `letter-spacing` of 0.
+
+```html
+<p style="letter-spacing: normal !important">
+	The toy brought back fond memories of being lost in the rain forest.
+</p>
+```
+
+#### Failed Example 4
+
+This `p` element has a [computed][] `letter-spacing` of 0.
+
+```html
+<p style="letter-spacing: initial !important">
+	The toy brought back fond memories of being lost in the rain forest.
+</p>
+```
+
+### Inapplicable
+
+#### Inapplicable Example 1
+
+There is no HTML element.
+
+```svg
+<svg xmlns="http://www.w3.org/2000/svg">
+    <text y="20" style="letter-spacing: 0.1em">ACT rules</text>
+</svg>
+```
+
+#### Inapplicable Example 2
+
+This `div` element has no text node child.
+
+```html
+<div style="letter-spacing: 0.1em !important; border-top: 1px solid black;">
+	<!-- empty div, border to make it "visible" -->
+</div>
+```
+
+#### Inapplicable Example 3
+
+This `p` element has no [visible][] text node child 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 4
+
+This `p` element has no [visible][] text node child 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 5
+
+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 `p` element has no text node child. The [computed][] value of the `letter-spacing` property of the `span` element is the [inherited][] value, that is the [computed][] value of its parent and therefore not [important][].
+
+```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 `p` element has no text node child. The [computed][] value of the `letter-spacing` property of the `span` element is the [inherited][] value, that is the [computed][] value of its parent and therefore not [important][].
+
+```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'
+[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'
+[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'
+[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'
+[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'