Description

   When you call LBR$INI_CONTROL, the Librarian sets the current
   library index to 1 (the module name table, unless the library is
   a user-developed library). If you need to process another library
   index, you must use LBR$SET_INDEX to change the current library
   index.

   Note that macro, help, and text libraries contain only one
   index; therefore, you do not need to call LBR$SET_INDEX. Object
   libraries contain two indexes. If you want to access the global
   symbol table, you must call the LBR$SET_INDEX routine to set the
   index number. User-developed libraries can contain more than one
   index; therefore, you may need to call LBR$SET_INDEX to set the
   index number.

   Upon successful completion, LBR$SET_INDEX sets the current
   library index to the requested index number. LBR routines number
   indexes starting with 1.