5eebb559_nd_for_the_PostScript_language__Purpose
[Key] FullLine [Purpose] 
Procedure to be executed when readline has returned true, meaning a newline was encountered, and the line read was of nonzero length. This can represent an entire full line in the input, or the final segment of a line after an embedded PostScript token. The stack contains (a) whatever was on it when \markup was invoked (except for the parameter dictionary), (b) as modified by any embedded PostScript tokens since, and not consumed by HandleToken or HandleResult, and (c) on top, the string just read. In driving a line-at-a-time text setting system, this procedure may invoke PartLine and then a library procedure to set the complete accumulated line; for a paragraph-at-a-time system, this procedure and PartLine will probably be the same. \markup fetches this value only once, so changing it from embedded PostScript code has no effect, but nothing stops the supplied procedure looking at other keys and having changeable behavior.
Markup: a minimalist markup frontend for the PostScript language
Purpose