The SGML Common package contains install-catalog, 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 contain the basic character entities defined with SDATA entries. XML entities files contain the basic character entities defined by a hexadecimal representation of the Unicode character number.