Related is the IDs for <form> elements: if you use <input id="foobar"> you can access foobar from DOM via form.foobar. This is OK until you use <button id="submit">, then all codes relying on form.submit() function does not work anymore (prototype function overshadowed by object property).
I stumped on the "feature" a while ago. I don't know if this behaviour is documented anywhere in the DOM specification. Might as well if somebody is working on a linter for HTML/DOM-related stuff, add a rule to disallow id which is names from Element or Window object.
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