[4e8ab6] Update assumptions and background per the survey (#2131)

* Update assumptions and background per the survey

* Tweak definitions

---------

Co-authored-by: Jean-Yves Moyen <jym@siteimprove.com>

Author: tombrunet

_rules/role-required-states-and-properties-4e8ab6.md

@@ -24,6 +24,7 @@ input_aspects:
 acknowledgments:
   authors:
     - Anne Thyme Nørregaard
+    - Tom Brunet
   funding:
     - WAI-Tools
 ---
@@ -38,21 +39,19 @@ For each test target, the [WAI-ARIA required states and properties][] for the ro
 
 ## Assumptions
 
-- The applicability of this rule is limited to [explicit semantic roles][explicit semantic role] based on an assumption that all native HTML and SVG elements have native attributes that are mapped to all of the [WAI-ARIA required states and properties](https://www.w3.org/TR/wai-aria/#requiredState) for the [implicit semantic role][] of the element.
-
-- The ARIA `role` is being used to comply to WCAG.
+- The ARIA `role` is being used to conform to WCAG.
 
 ## Accessibility Support
 
-This rule relies on browsers and assistive technologies to support leaving out [WAI-ARIA required states and properties][] when a [WAI-ARIA implicit value for role][] is specified in [WAI-ARIA Specifications](#wai-aria-specifications).
+This rule relies on browsers and assistive technologies to support leaving out [WAI-ARIA required states and properties][] when a [WAI-ARIA implicit value for role][] is specified in [WAI-ARIA Specifications][].
 
 **Note:** The required states and properties with implicit values can be found in the Core Accessibility API Mappings 1.1 [Overview of default values for missing required attributes](https://www.w3.org/TR/core-aam-1.1/#authorErrorDefaultValuesTable).
 
 ## Background
 
-Omitting required ARIA properties is often the result of a developer error. When required properties are missing some browsers and assistive technologies will guess the property, or leave the element inaccessible.
+Omitting [WAI-ARIA required states and properties][] is often the result of a developer error. When required properties are missing and a default value is not specified by [WAI-ARIA Specifications][], the behavior is not defined. For [WAI-ARIA 1.2][], the only [explicit semantic roles][explicit semantic role] with a required property with a default value are the `option` and `tabs roles` for the `aria-selected` property.
 
-This rule is testing author built components, not user-agent built ones. Elements that keep their [implicit semantic role][] are mapped into conforming accessible objects, with all required properties, by user agents and are therefore not tested by this rule. Most of these mappings are defined in the [HTML Accessibility API Mappings, Attribute State and Property Mappings](https://www.w3.org/TR/html-aam-1.0/#html-attribute-state-and-property-mappings).
+This rule is testing author built components that specify [explicit semantic roles][explicit semantic role] and not components that keep their [implicit semantic role][]. For components that keep their [implicit semantic role][], all native HTML and SVG elements have native attributes that are mapped to all of the [WAI-ARIA required states and properties](https://www.w3.org/TR/wai-aria/#requiredState). Most of these mappings are defined in the [HTML Accessibility API Mappings, Attribute State and Property Mappings][html aam].
 
 ### Bibliography
 
@@ -221,9 +220,11 @@ This `combobox` is not [included in the accessibility tree][] due to its styling
 ```
 
 [explicit semantic role]: #explicit-role 'Definition of explicit semantic role'
+[html aam]: https://www.w3.org/TR/html-aam-1.0/#html-attribute-state-and-property-mappings 'Specification of HTML attributes value mapping to ARIA states and properties'
 [implicit semantic role]: #implicit-role 'Definition of implicit semantic role'
 [included in the accessibility tree]: #included-in-the-accessibility-tree 'Definition of Included in The Accessibility Tree'
 [wai-aria required states and properties]: https://www.w3.org/TR/wai-aria-1.2/#requiredState
+[wai-aria specifications]: #wai-aria-specifications 'Definition of WAI-ARIA Specifications'
 [wai-aria implicit value for role]: https://www.w3.org/TR/wai-aria-1.2/#implictValueForRole
 [wai-aria 1.2]: https://www.w3.org/TR/wai-aria-1.2/
 [html or svg element]: #namespaced-element