From W3C Wiki
The role attribute supplies metadata about the intended semantic meaning of an element.
This page provides a registry for roles in order to promote interoperability.
Standard TTML Roles
The above roles are standard values, defined by the TTML Recommendation. Note that all roles that do not start with x- are reserved for standardization.
Custom TTML Roles
- x-definition indicates the parent element of a term and its gloss
- x-term Indicates the marked text to be a defined term.
- x-gloss Indicates the marked text to be gloss text for a defined term - for example, to be styled as Japanese furigana using CSS3 ruby style (preliminary until CSS3 is finalised)
- x-gloss-paren Indicates the marked text to be a marker character around gloss text for a defined term
- x-extended-description Indicates that the marked text, if read out as audio (whether pre-recorded or generated from text), may have a duration longer than the elements active duration. User agents may alter the playback of external media to compensate.
- x-nav-section Indicates the marked text may be interpreted as a media reference equal to to the computed start time of the element.
- x-hyperlink Indicates the marked text may be interpreted as a link to an external resource