Include is an option in bzflag mapping that allows you to specify a second bzw file that will be included in the first bzw. Both files are then loaded by bzfs as a single bzw. It is very easy to use, just put this in the first bzw.
Include can be used in many ways. It has proved very useful when several mappers are all working on a single map, and mappers frequently exporting from applications such as Wings3D have found it useful to maintain a separate materials file, as these can often overwrite any image URLs at export. Some people have used includes to isolate regularly modified parts of a map file, for ease of changing. As an example, the material definitions for the Planet MoFo Billboards are stored in a separate file so they can be changed quickly.