HTML Text Alternatives document question

The text alternatives document [1] has a number of places where it says
"accessibility supported".  As in "Once figure and figcaption are
accessibility supported...".  Is this a term that we use a lot?  Is it well
defined / known?  It feels awkward to me and it isn't in the glossary.
Thoughts?

[1] https://w3c.github.io/alt-techniques/

-- 
Shane McCarron
Managing Director, Applied Testing and Technology, Inc.