On Export to HMTL? I looked at the files, but it was not obvious to me what it does.
I think, without having tested, this applies the menu item "Hide >" (you may have to widen your window to reveal it) to all messages in the export. It strips out the quoted messages from message replies when prefaced by ">" or other demarcation. In the Help page, look at "Hiding old posts".
Now that I've tested the "Apply Hide function before export", I confirm that it does what I say and more... too much more in my case. The metadata of each post is gone for most posts, the remaining text may be weirdly formatted and possibly scrambled, chunks of text from ostensibly the original posts are missing, and there may great globs of HTML code scattered among the content. The concept is great but I won't risk it.
Yeah. Its a bit hit & miss.
The idea is that if you *really* want to export to HTML & trim replies then this gets you part of the way there.
Its better than the alternative which is manual trimming.
Cheers,
Wilson.