Captioning verbiage for the Text Spacing Understanding doc

Hi John,

At the November 13, 2017 AGWG teleconference, you mentioned that the Text
Spacing Understanding doc should have verbiage to explain what types of
captions are not expected to adapt to the SC's metrics [1].

I put a place holder in the document [2] so it wouldn't fall through the
cracks. Would it be possible for you please suggest appropriate verbiage to
use?

We are very fortunate that you have deep expertise in captioning. Thank you
very much for your consideration.

Kindest Regards,

Laura

[1] http://rawgit.com/w3c/wcag21/master/guidelines/index.html#text-spacing
[2] http://rawgit.com/w3c/wcag21/master/understanding/21/text-spacing.html