exclude #ifdef regions when using gtags

Hi all,

is there a way to instruct gtags to disregard parts of source files that are
encapsulated by a certain #ifdef/'endif preprocessor command? In my case the
sources I got contain plain text that is used for a proprietary
documentation tool. The text is encapsulated in

   #ifdef XXX_DOCUMENTATION

   #endif

These #ifdef/#endif are not nested.

I would hate to remove these comments from the source files because they
contain valuable information that then wouldn't show up in the browsable
source files created by htags. I just want gtags to ignore them.

Thanks,
Ruppert

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