HP 3000 Manuals

HP RPG/XL Utilities-Part 1 XSORT

Programming with ALTSEQ 

Placing an alternate character in the sequence position which is normally
assigned to another means that both occupy the same position and are
considered equal.  (See Sample ALTSEQ Statements section in this
chapter.)

If you do not want to have the characters regarded as equal, the one
which normally occupies that position must be moved.

MPE/iX 5.0 Documentation