MesQuilla

"Is it possible to combine header regex's in one expression"

If by that you mean the text that you enter into the filter action, that text is just sent directly to javascript. If it is valid in javascript, it should work. If not, then not. You should always be able to add multiple independent search terms with an OR though.

"I have been trying to find in TB source, internet etc the possible values for StatusOfset in Header Regex – which I assume holds values for read, unread, forwarded etc, but can't find any references to what these values are when using this regex"

StatusOfset is "offset in a local mail message of the mozilla status hdr" The misspelled "StatusOfset" is the property name in the mork database. I consider this quite obscure and internal to mailnews code, so I don't know what you are trying to use this. You cannot get status fields from a regex of this. I also don't know why you would want to use a regex to access status fields, since there are more direct ways of using those in search terms.