1.  This section includes a number of mechanisms for embedding content, but the <img> and <area> elements are the only elements that include a specific mechanism for providing a short text alternatives (@alt). The need for a mechanism to include a short text alternative (label) for the embedded content is no different for elements such as embed, video, audio, canvas, MathML and SVG. Since the ability for the embedded content to provide a text alternative directly will vary across formats, content types and authoring practices, HTML5 should include support for the alt attribute or a similar mechanism (ex. aria-labelledby) for each of these elements and the conformance requirements regarding its presence should be consistent for each element.

2. From an accessibility perspective, HTML5 should describe a model for fallback content that allows the user to choose from any available fallbacks. The problem with specifying that fallback content should only be "used when an external resource cannot be used", is that it puts users in the position of having to guess about the accessibility of the content on different sites and to reconfigure their browser to find out if they guessed correctly. For example, an author on one site might embed captioned video that requires a plugin in order to be rendered with no fallback while an author on a second site uses the same plugin to include a video, omits captions, but provides fallback content that includes a text transcript of the video. The problem is that a deaf user who has the required plugin installed will get the captions on the first site, but will likely miss that there's no fallback on the second site entirely. Similarly, if the same user does not have the required plugin (or has turned it off so that they could access fallback content on another site), they end up getting nothing on site 1 and the fallback content on site 2.