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 /path/to/file.bzw
Include can be used in many ways. When several mappers are all working on a single map, it has proved very useful. Mappers using Wings3D have found it essential in maintaining a separate materials file, as Wings3D overwrites any image URL's at export.