SC4-1-1+SC4-1-2-aria-allowed-attribute (#257)

* Create SC4-1-1+SC4-1-2-aria-allowed-attribute.md

* Editorial updates

* Editorial updates per feedback

* Adding a note about scope of rule

_rules/SC4-1-1+SC4-1-2-aria-allowed-attribute.md

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+---
+name: ARIA allowed attribute
+description: | 
+  This rule checks that `aria-*` attributes are allowed for the element they are specified on.
+
+success_criterion:
+- 4.1.1 # Parsing (A)
+- 4.1.2 # Name, Role, Value (A)
+
+test_aspects:
+- DOM Tree
+- CSS Styling
+
+authors:
+- Anne Thyme Nørregaard
+---
+
+## Test procedure
+
+### Applicability
+
+Any attribute that is specified on an HTML or SVG element where the attribute name starts with `aria-`.
+
+### Expectation
+
+The target attribute is either listed under [WAI-ARIA 1.1 Supported States and Properties](https://www.w3.org/TR/wai-aria-1.1/#states_and_properties) for the [semantic role](#semantic-role) of the element that the attribute is specified on, or it is found on the list of [WAI-ARIA 1.1 Global States and Properties](https://www.w3.org/TR/wai-aria-1.1/#global_states).
+
+**Note:** Assessing the value of the attribute is out of scope for this rule.
+
+## Assumptions
+
+*There are currently no assumptions*
+
+## Accessibility support
+
+*There are no major accessibility support issues known for this rule.*
+
+## Background
+
+- [Understanding Success Criterion 4.1.1: Parsing](https://www.w3.org/WAI/WCAG21/Understanding/parsing.html)
+- [Understanding Success Criterion 4.1.2: Name, Role, Value
+](https://www.w3.org/WAI/WCAG21/Understanding/name-role-value.html)
+- [WAI-ARIA 1.1, Supported States and Properties](https://www.w3.org/TR/wai-aria-1.1/#states_and_properties)
+- [WAI-ARIA 1.1, Global States and Properties](https://www.w3.org/TR/wai-aria-1.1/#global_states)
+
+## Test Cases
+
+### Passed
+
+#### Passed example 1
+
+`aria-pressed` attribute is allowed for role `button`.
+
+```html
+<div role="button" aria-pressed="false"></div>
+```
+
+#### Passed example 2
+
+`aria-pressed` attribute is allowed for `role=button` that is the implicit role for `button` element.
+
+```html
+<button aria-pressed="false"></button>
+```
+
+#### Passed example 3
+
+Global state that is supported by all base markup elements.
+
+```html
+<div aria-hidden="true"></div>
+```
+
+### Failed
+
+#### Failed example 1
+
+`aria-pressed` attribute is not allowed for role `checkbox`.
+
+```html
+<div role="checkbox" aria-pressed="false"></div>
+```
+
+#### Failed example 2
+
+`aria-pressed` attribute is not allowed for `role=checkbox` that is the implicit role for `input` elements of type `checkbox`.
+
+```html
+<input type="checkbox" aria-pressed="false">
+```
+
+### Inapplicable
+
+#### Inapplicable example 1
+
+No attribute that starts with `aria-`.
+
+```html
+<div role="region"></div>
+```