The libxml extension is enabled by default, although it may be disabled with --disable-libxml.
The optional --with-libxml-dir
directive is used to specify the location of libxml
on the system that PHP is being compiled on, otherwise only the
default locations are scanned. The configure process
checks for libxml (specifically, xml2-config) in the
following order:
The location ([DIR]) specified with --with-libxml-dir ([DIR]=/bin/xml2-config)
/usr/local/bin/xml2-config
/usr/bin/xml2-config
If configure cannot find xml2-config in the directory
specified by --with-libxml-dir, then
it'll continue on and check the default locations.