Markup Validity

Topic	Technique	WCAG AA Requirement
Unique Identifiers	Unique IDs: IDs MUST be unique within a web page.	Required WCAG 4.1.1
	Unique Names: The "accessible names" of elements, when provided, of block level elements (e.g. landmarks, tables, iframes, etc.) SHOULD be unique within a web page.Note: The accessible name is determined by attributes or elements such as aria-label, aria-labelledby, alt, <caption>, etc.	best practice
	One Attribute Instance: Elements MUST NOT contain more than one instance of the same attribute.	Required WCAG 4.1.1
Well Formed	Closing Tags: Elements must not be missing closing tags. DIV or P element must not be nested within a LABEL element. Element must not contain duplicate attributes.	Required WCAG 4.1.1
Nesting and Relationships	Parent-Child Relationships: Markup MUST adhere to required parent-child relationships of elements and attributes.	Required WCAG 4.1.1
	ARIA relationships: ARIA relationships (e.g. parent-child, aria-owns, etc.) SHOULD adhere to WAI-ARIA Authoring Practices	Required WCAG 4.1.1
Deprecated Markup	Deprecated Markup should not be used.	best practice