Thank you for the answer. I understand that the way Geany find a folding point is to parse the syntax.
I wonder if Geany had an option to make a folding point *according to the indentation*. This will enable .txt files to be folded in a very sensible way. I also think this would not be technically challenging too much, since Geany already detects indentation fairly well.
Some editors like EditPlus (proprietary, www.editplus.com) have that option, and it is great to get a neat folded view, not only of the code, but also of the results of a program, which often have an arbitrary structure.
Furthermore, you don't even need a syntax file to fold a file of a new type, if you only indented it appropriately.
Maybe I should suggest this as a feature request.
HR Kang.