Editorial changes to SC

Following up on the QA checklist I sent around last week, I have done an 
editorial pass of the SC in WCAG 2.1. The changes I made are shown in:

https://github.com/w3c/wcag21/commit/19ac37387f3c8a82c5d3838b9fa5327b28b37dab

Please let me know if you disagree that any of these changes are 
editorial. Most are simple things like punctuation, but in a couple 
places I moved clauses around to improve coherence and readability.

I added a couple things to the QA checklist as I went, and implemented 
those in these edits:

https://www.w3.org/WAI/GL/wiki/index.php?title=WCAG_2.1_QA_Checklist&diff=8139&oldid=8109

The change that I think might give people the most pause is Content on 
Hover or Focus 
(https://w3c.github.io/wcag21/guidelines/#content-on-hover-or-focus), 
where I changed

    "When content becomes visible when triggered by a user interface
    componentreceiving keyboard focus or pointer hover, the following
    are true, except where the visual presentation of the content is
    controlled by the user agent and is not modified by the author:"

to

    "When a user interface componentwhich receives keyboard focus or
    pointer hovercauses content to become visible, the following are true:"

and moved the exception to after the bullet list. I made this change 
because I was finding the dependent clauses to be very hard to follow. I 
think I didn't change meaning, but want to point this out for extra 
review in case you disagree this change was editorial.

I plan to make a pass through terms as well but didn't get to that today.

Michael