I have a friend who has the specific problem of building a case against the use of a custom HTML <wrapper> tag in some site's markup. Now, intuitively we can answer that use of such a tag is risky, as future HTML specs may define a wrapper tag with semantics that conflict with its use on the site. We can also appeal to a particular section of the HTML5 spec which also recommends against the use of custom tags for this reason.

And while I agree with the conclusion, I find these arguments a little on the weak side, on their own. Is there some well grounded and proven theory in computer science from which we can derive this conclusion? Have programming language theorists created proofs about the properties of vocabulary versioning, or some such thing?