Addendum FYI: The history from the previous owner of the chatroom is 48 months, with the average size of each months HTML file being about 80kb, with largest about 220kb.
So at present, I have 60 files to scan. And my users are patient, so a bit of delay to accomplish the search is ok.
It certainly beats the current situtation, which is browsing EACH months history one-by-one and doing search via "Find"!