Programmatic label

Element L is a programmatic label of target element T if either:

• T is a labeled control of L; or
• L is referenced by ID in the aria-labelledby attribute of T.

Note: a given element may have more than one programmatic label.

Explicit label

The labeled control L of an element T is its explicit label if L has a for attribute referencing T's id attribute.

Implicit label

The labeled control L of an element T is its implicit label if L has a no for attribute and is an ancestor of T in the DOM tree. Note that explicit labels take precedence over implicit label, and that labeled controls do not cross shadow boundaries nor content documents.