declaration/definition
library (public-identifier system-identifier)+
The library declaration is used to map the public identifier of an SGML/XML external text entity to a system identifier (system filename containing replacement text). In the library declaration, the public-identifiers and the system-identifiers are quoted strings:
  library "-//ES//DTD for foo//EN" "foo.dtd"
          "-//ES//TEXT for bar//EN" "bar.txt"
          "-//ES//TEXT for baz//EN" "baz.txt"
          "-//ES//TEXT for bat//EN" "bat.txt"
There can be any number of library declarations in a program, but each public-identifier should have only one definition. 
Note that library declarations can be put into a separate file, external to the main program, which can be referenced using the "-library" command-line option. Entries in the library file always take precedence over those in the OmniMark program. 
OmniMark will look for the system identifier in the following order: