[Help] add `iframe` & video to Help page for `frame_src_valid`

[philljenkins]

• the Help should be improved to include both <frame’s and <iframe’s since the rule logic covers both
• validate the references
• add a reference on verifying the content if it is video

as-is Help:

Verify content is accessible

• A <frame> containing non-HTML content must be made accessible
• Rule ID: frame_src_valid
• Reason ID: Potential_1

What to do

• HTML <frame> is obsolete, if possible avoid its use
• Or, verify that interactive content inside the frame is accessible by keyboard
• And, verify that content inside the frame can be accessed by assistive technologies, such as a screen reader

Background

See Slack discussion
https://ibm-studios.slack.com/archives/C036P1CTN/p1753718317230469?thread_ts=1753447906.635229&cid=C036P1CTN

[philljenkins]

Add the example to the help if the content is a video player and video:

• If the content in the <iframe> is video: Verify the video & player are accessible.
  • Do this by reviewing and meeting the 7 requirements in the Planning for video.

[MHoov]

Tom to add some comments after we finish reviewing issues.

[tombrunet]

<frame> is now an obsolete HTML element, which is why it is not addressed in the help.

The issue is generic about the content of the iframe provided it's "html", but various content types like video can be wrapped in an html page by the browser. It doesn't make sense to me to point to video as a specific content type in the help and ignore all of the other content types.

The help may need more elaboration on why this rule is firing (or maybe we need to narrow the scope if it's firing on ALL iframes that point to html docs to just those we can't access), but I'm not understanding why we would specifically reference video topics.