xmlcatmgr is a command line script used to manipulate SGML and XML catalogs.
It is designed with simplicity in mind:  it does not depend on external
programs nor libraries, so it is ideal to manage catalog files from inside
pkgsrc.  It is also useful to handle shared directories like share/sgml and
share/xml.

XML catalogs are files that contain mappings from public identifiers to
system identifiers.  This allows XML parsers to locate public identifiers
in the local system.