The SGML Common package contains
sgmlwhich, SGML entities
files and XML entities files.
install-catalog creates a centralized catalog that
maintains references to catalogs scattered throughout the
/usr/share/sgml directory tree.
sgmlwhich will print to standard output the name of
the main configuration file.
SGML entities files
SGML entities files contain the basic character
entities defined with SDATA entries.
XML entities files
XML entities files contain the basic character
entities defined by a hexadecimal representation of the Unicode character