I've never heard of it either. I can only assume it means that your HTML tags don't line up? I really don't know ... For all things HTML, my first bet would be the www.w3c.org - the World Wide Web Consortium.
I found this on an exam paper I am revising with. its in the section of hypertext linksThe question is:
What is the problem of "HTML dangling". Give the key points of the solution to this problem: Uniform Resource Name.
Well, given that at least 2 seasoned Web Developers with likely over 30+ years combined experience have never even heard of the term, I would say the exam is screwy. Even the term "Universal Resource Name" is a bit off. There are URIs and URLs, (Universal Resource Indicators & Universal Resource Locators), but not URNs.
If you are revising the exam, just strike that question entirely.
Also, be careful what you end sentences, err,... with.
"A URN (Uniform Resource Name) is an Internet resource with a name that, unlike a URL, has persistent significance - that is, the owner of the URN can expect that someone else (or a program) will always be able to find the resource. A frequent problem in using the Web is that Web content is sometimes moved to a new site or a new page on the same site. Since links are made using Uniform Resource Locators (URLs), they no longer work when content is moved.
A URN looks something like a URL. For example, here's a hypothetical URN:
Thanks for all your help, someone has suggested that I look at dangling links or broken links as they think thats what the exam paper is referring to. Will also look at the link you provided.