Text that will not match a search, will not wrap where it should, or breaks a trigger for no visible reason usually contains a character you cannot see. This marks every one of them in place and explains what each does, so you can find the cause rather than retyping the line and hoping.
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It renders your text with every problematic character marked in place, and lists what it found, how many times, and on which lines. Non-breaking spaces, zero-width spaces, byte order marks, soft hyphens, word joiners, curly quotes, control characters and the rest.
The Text Cleaner will strip these out in one pass. This one exists for the moment before that, when you do not yet know what is wrong. A search that fails on a word plainly visible on screen, a line that will not wrap, a trigger that works everywhere except one slide: those all have the same family of causes, and the fastest route to the answer is to look at the characters.
A non-breaking space is the most common, because Word inserts them and they survive every paste. It looks exactly like a space and stops a line wrapping. A zero-width space is the most frustrating, because it is genuinely invisible and splits a word so that searching for it fails. A curly apostrophe is the most expensive, because it breaks JavaScript triggers and the error message never mentions it.
It flags characters that are unusual in course copy, not characters that are wrong. A course written in French will contain narrow non-breaking spaces before its punctuation and they belong there. Treat the list as things worth knowing about rather than a list of faults.