I understand that, I just wanted to edit font-sizes (to be compatible).
1 => 8 ... It's substitution? For example, could I write 150 => 16, so that size 150(% in pphBB) would be size 16 here?
By the way, BBCode for underlined text seems to be the same both for phpBB and IPB. However, it's not working properly (see Spoiler 1).