Issue with guideline 2.11

Hi,

I noticed an error in guideline 2.11. In the summary, each criterion is
identified (e.g. stop/pause/resume 2.11.5). However there is a mismatch
starting at 2.11.8. In the summary, 2.11.8 should describe enabling and
disabling of tracks while 2.11.9 should address contrast adjustments.
However in the following details section, there is no content about tracks,
2.11.8 is used to describe contrast and 2.11.9 is not listed.

That criterion is very important because it likely address captions and
audio description of timed media.