Out of curiosity, could you give an example/explanation of some input that makes this condition return true?

Also, why does this still run when the SANITIZE_DOM config option is false? I was under the impression that setting SANITIZE_DOM to false disables any clobbering-related checks. Is that not the purpose of SANITIZE_DOM? If not, what's the purpose?

Lastly, is it strictly necessary to get the value of elm.textContent in order to ensure it isn't clobbered? The textContent getter is really relatively slow. For large node trees, sanitization can be very noticeably slow just because of that one check (which I know because I profiled it).