HTML5 allows elements to have IDs that contain colons, ex:
<div id="#this:isvalid"></div>
However, because this library is using document.querySelector, it is going by CSS selector rules, so a colon in the ID would need to be escaped before calling querySelector, otherwise it would fail with error:
Uncaught DOMException: Failed to execute 'querySelector' on 'Document': '#this:isvalid' is not a valid selector.