5eebb559_nd_for_the_PostScript_language__Purpose
[Key] EOFToken (optional) [Purpose] 
When the end of SourceFile has been reached, ordinarily \markup completes. If this entry is present, its value is treated just as if it had been returned by token at the end of the file; HandleToken and HandleResult are executed, and if stop was not executed, reading resumes from the (presumably changed) SourceFile. This is the mechanism by which a file-inclusion operation can be supplied. The idea is for the file-include procedure to store the new file in SourceFile and supply an EOFToken that restores the old one (and the old EOFToken). Such a procedure can be generated by includegen, which is used to provide the file inclusion feature in Basic. If there is an EOFToken and it does not either replace SourceFile, replace EOFToken, or execute stop, \markup will reach end of file and spin.
Markup: a minimalist markup frontend for the PostScript language
Purpose