In pretty much every program I use, # at the start of a line means that the rest of the line is a comment. That's useful, not only for comments, but also for temporarily disabling a line.
In bind a ; at the start of a line signifies a comment, and it doesn't recognise a #
Oh, but it's more subtle than that. You can use # for a comment in the named.conf file. But not in the zone files.
It gets me every time. I make a change in my DNS files, perhaps commenting out a line, and then the DNS doesn't work becuase I used # instead of ;
Please, O people who maintain bind, allow # to start a comment line.