Rule: Attributes that start with `aria-` must be defined.

Rule ID	Widget 5
Conformance	Required
Definition	Elements with the attributes that start with `aria-` must be a valid ARIA property or state.
Purpose	ARIA attributes must be defined properties or states to accurately describe web content to users of assistive technologies, especially screen reader users
Conformance	Required
WCAG Success Criteria	Success Criterion 4.1.2 Name, Role, Value Other Related Success Criterion: Success Criterion 1.3.1 Info and Relationships Success Criterion 3.3.2 Labels or Instructions
Rule Category	ARIA Widgets
Rule Scope	Element
Techniques	Use defined ARIA properties and states in the ARIA specification. Check W3C WAI Accessible Rich Internet Applications specifications for allowed values for ARIA attributes.
Information Links	Accessible Rich Internet Applications (WAI-ARIA) 1.2 Specification: Supported Property and States G108: Using markup features to expose the name and role, allow user-settable properties to be directly set, and provide notification of changes ARIA5: Using WAI-ARIA state and property attributes to expose the state of a user interface component ARIA Authoring Practices MDN Web Docs: ARIA Web Fundamentals: Introduction to ARIA

Rule: Attributes that start with aria- must be defined.