What elements can a span tag contain in HTML5?

So I have been a CLI or Cron developer in PHP for most my career and now I am learning why I did not like UI work in school ;) I am dealing with HTML5 validation here and I am not finding an answer to a question that is for curosity. I ran the W3C HTML5 validation on my home page and I got several errors around a div being within a <span> and that is not allowed. I tried changing all <div> within spans to a <p> but recieve pretty much the same error. http://www.w3schools.com/html5/tag_span.asp does not explicitly say what elements are allowed within a <span> and neither does the error from the validator:

Line 85, Column 69: Element p not allowed as child of element span in this context. (Suppressing further errors from this subtree.)

2 questions:

1) What elements if any are allowed within a <span>?

2) Where can I reference for what elements are allowed within another? I have googled but see nothing that has a "W3C" stamp on it.

Solution 1:

Only inline elements may be contained within inline elements. span is an inline element. So, tags like a, img, sup, etc. can go within a span, but block level elements like div and p cannot.

UPDATE

In reality, different elements which default to inline display behave differently. Some "inline" elements may allow block elements (a for example), while others don't (like span).

If you're interested in what an HTML tag may contain, your most official source is the WHATWG page on HTML elements. You can check any HTML element and see what content is permitted (see 'Content Model' for each element):

http://www.whatwg.org/specs/web-apps/current-work/multipage/#auto-toc-4

Here's the definition of the span tag, which indicates that only 'phrasing' content is allowed.

http://www.whatwg.org/specs/web-apps/current-work/multipage/text-level-semantics.html#the-span-element