Does it make semantic sense to use H1,H2,H3 in web applications?

Question

I have a web application, that can be embedded in other peoples web sites, inside an iframe.

I don't know the layout of their web sites, so I wouldn't know which level of header element (<h1>, <h2>, <h3>, etc.) to start with in my web application.

According to this page, you can "reset" the headers by sectioning the content (using <article>, <section>, <nav>, or <aside>), starting with <h1>. Does it make sense to wrap a web application inside a <section>?

And should I even be using <h1>, <h2>, <h3>, etc. at all, inside a web application?

Note that accessibility is of importance in this web app. (WCAG 2.0 AA).

Answer 1

Your question makes sense only if the iframe is inserted seamlessly (which is something that is not implemented in standard browsers, and has disappeared from HTML5.1) :

In speech media, the user agent should render the nested browsing context without announcing that it is a separate document.

User agents should, in general, act as if the active document of the iframe's nested browsing context was part of the document that the iframe is in.

If it's not the case (and it surely is not), you have to consider the iframe as a separate document, starting from h1 because it opens a new context.