If you want to tailor Quickscript, modifying how existing layout marks work or creating new layout marks, you will need to understand how the Quickscript machinery processes layout marks.
Quickscript contains a table
an array of arrays. Each array within Kwrd contains three items:
|First element in a Kwrd item||The keyword string, eg. (FN), identifying the keyword.|
|The second element in a Kwrd item||The keyword procedure, which
will be run to implement the keyword.
The text following the keyword string is put on top of the stack before the procedure is run. That is, a layout mark %FN,Cou% will match a keyword string of (FN), and (,Cou) will be put on the stack to be available to the procedure. A layout mark %FN% will also match (FN), and the empty string () will be put on the stack before running the procedure.
|The third element in a Kwrd item||The keyword flags, indicating
how the keyword is to be processed and
when the procedure is to be run. The flags are built as bitwise-OR of the following
Quickscript processes all layout marks until
In cases 1) or 2), the input stream is now processed word at a time, each word being measured to see if it will fit on the current line. The accumulated text is output when the output line is filled, or when a "line-breaking" or "start-recording" layout mark is encountered. A "line-breaking" mark will cause the input text to be processed again keyword by keyword.
In case 3), the input stream is recorded to RecBuf, being checked for layout marks that have "start-recording" or "end-recording" status. Any other layout marks are simply included with the text in RecBuf. RecBuf is cleared when an "end-recording" layout mark causes the count of recording marks to be decremented to zero. It is possible by this scheme to record text for multiple purposes, but only one buffer is used and the text is recorded from the first "start-recording" mark, for use when an "end-recording" mark is found.
At the start of Quickscript execution, it places a number and a mark on the stack. At various stages during its execution, other information is put on the stack beneath the mark, with the number changed accordingly. This means of recording internal state information should not be interfered with in any PostScript included within a Quickscript document, for the effects will be unpredictable.
When embedded PostScript is executed, the current point is recorded beneath the mark, so if the embedded PostScript finishes with no current point existing, it can be recovered from the stack.