In an effort to write more expressive HTML, I feel custom HTML elements are a good way for any webapp or document I may write to have good meaning gleamed from the tag name itself without the use of comments.
It appears I can define a custom HTML element with:
The problem with what you're trying to do is not that we can tell you it will break in some expected ways. It's that when you deviate from standards in this way, no one knows what to expect. It is, by definition, undefined, and the behavior of browsers that see it is also undefined.
That said, it might work great! Here's the things to keep in mind:
registerElementcomes into play, which can take an HTMLUnknownElement and make it known.
Browsers have a long history of taking whatever you give them and trying to do something reasonable with it, so you're likely to be OK, and if you are interested in primarily targeting HTML5 browsers, then you're very likely to be OK. As with everything HTML related, the only universal advice is to test your target demographic.