This is an inbuilt function function provided by PPWIZARD.
This routine takes a single parameter which is the include level that you are interested in. The line number being processed of the input file at that level is returned.
If you don't pass any value then the current level is assumed. If you pass an invalid value the empty string ("") is returned.
This rexx routine does a similar job to the "<?InputComponentLine>" special variable (but for any level - not just the current one).
For an example of how it could be used have a look at the InputComponentLevel() routine.