Thank you, I had a look and found there’s a bunch more of regexp that I have to read up on !! I have a habit of using those cumbersome search-replace to work around difficult spots in TW, in regexp and in title/list operations. TW actually has regexp escape and comes in useful for that, thanks!
I wish there are “title escape/unescape” operators also, because TW’s list operations are intended to process titles of tiddlers, and are use for general string/text processing as well, but break when dealing with more complex text/wikitext with double square brackets, line breaks and such.