13.5 Optional Features
Some packages pay attention to `--enable-feature' options
configure, where feature indicates an optional part
of the package. They may also pay attention to
`--with-package' options, where package is something
like `gnu-as' or `x' (for the X Window System). The
`README' should mention any `--enable-' and `--with-'
options that the package recognizes.
For packages that use the X Window System,
usually find the X include and library files automatically, but if it
doesn't, you can use the
`--x-includes=dir' and `--x-libraries=dir' to
specify their locations.