[syslog-ng] Which macros are available for filtering ?

On a test machine, I've set up syslog-ng with a filter which looks like this : filter filter1 { match(".+" VALUE ("MACRO")); }; I've tried many MACROS and it seems only a few of them are not empty (easy to spot using this regex). The most surprising is that several documented macros are empty : for instance, MSGHDR and MSG (MSG should be the same than MESSAGE, but looks like it's not). Is it a bug ? Thanks,