Any docs on callback return value meanings?

["Daniel J. Kressin" <kressd11 sol acs uwosh edu>]

Are there any docs available that describe what the meanings of returning
true/false from callbacks are?  For example, my configure callback returns
true while my expose callback returns false -- Why?

Dan 
 ____    Kressin   ____   .-----------------------------------. 
/___ \____________/ __ \  | dkressin@acm.org                  |
    \  \    /      /  \ | | Lead Programmer/Analyst           |
 ___/ __\/\/rench_ \__/ | | University of Wisconsin - Oshkosh |
\____/            \____/  | www.mio.uwosh.edu/~kressd11/      |
                          `-----------------------------------'