Changes Unknown when pulling b9ec717 on issue_8 into * on master*.

first, I think we must focus on WCAG 2.0 only:

WCAG 2.0 succeeds Web Content Accessibility Guidelines 1.0, which was published as a W3C Recommendation May 1999. Although it is possible to conform either to WCAG 1.0 or to WCAG 2.0 (or both), the W3C recommends that new and updated content use WCAG 2.0. The W3C also recommends that Web accessibility policies reference WCAG 2.0.

second, I'm not sure what's the best approach here.

I tested 4 of the most important providers (SlideShare, SoundCloud, Vimeo and YouTube); all of them use an iframe, all of them include a title in the iframe and all of them provide an alternate link for browsers/devices not supporting the iframe tag.

as you can enter any code on the embed_html field I think we must only show a warning message after the user has saved the object; this way you'll give the opportunity to fix it.

for the WC3 fixes, obviously I did not explain myself it clearly: I never mend to remove the attributes from external code, just from our own templates.

see https://github.com/simplesconsultoria/sc.embedder/blob/master/src/sc/embedder/content/templates/embeddervideojs.pt#L54

enforcing content for WCAG 2.0 compliance is going to be harder and is the scope of a different package, IMO (collective.wcgawatchdog?).