EDIT on 1): after trying umpteen permutations of pattern, extension and coding in the post, I chanced on one that worked. Still am clueless about the principles.
on 2) I tried your suggestion but no success. It seems to me that the only bbcodes that I have been able to add are those with just one variable. Everything else just doesn't get interpreted. I have read the various posts around here but they didn't help. Is there any other information on how this interpretation works that could help me understand?
Any further help is appreciated! TIA!