The command tt(CHDIR) takes one argument, a directory to change to. This 
command is implemented to simplify the working with tt(includefile) (see 
tt(includefile) in tt(yodlmacros(7))). 
As a demonstration by example, consider the 
following fragment:

verb(\
includefile(subdir/onefile)
includefile(subdir/anotherfile)
includefile(subdir/yetanotherfile))

This fragment can be changed to:

verb(\
CHDIR(subdir)
includefile(onefile)
includefile(anotherfile)
includefile(yetanotherfile)
CHDIR(..))

The current directory, as given to tt(CHDIR), only affects how tt(includefile) 
will search for its files.
