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(dvips.info)PostScript hooks

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PostScript hooks
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  Besides including literal PostScript at a particular place in your
document (as described in the previous section), you can also arrange to
execute arbitrary PostScript code at particular times while the
PostScript is printing.

  If any of the PostScript names `bop-hook', `eop-hook', `start-hook',
or `end-hook' are defined in `userdict', they will be executed at the
beginning of a page, end of a page, start of the document, and end of a
document, respectively.

  When these macros are executed, the default PostScript coordinate
system and origin is in effect.  Such macros can be defined in headers
added by the `-h' option or the `header=' special, and might be useful
for writing, for instance, `DRAFT' across the entire page, or, with the
aid of a shell script, dating the document.  These macros are executed
outside of the save/restore context of the individual pages, so it is
possible for them to accumulate information, but if a document must be
divided into sections because of memory constraints, such added
information will be lost across section breaks.

  The single argument to `bop-hook' is the physical page number; the
first page gets zero, the second one, etc.  `bop-hook' must leave this
number on the stack.  None of the other hooks are passed arguments.

  As an example of what can be done, the following special will write a
light grey `DRAFT' across each page in the document:

     \special{!userdict begin /bop-hook{gsave 200 30 translate
     65 rotate /Times-Roman findfont 216 scalefont setfont
     0 0 moveto 0.7 setgray (DRAFT) show grestore}def end}

  Using `bop-hook' or `eop-hook' to preserve information across pages
breaks compliance with the Adobe document structuring conventions, so
if you use any such tricks, you may also want to use the `-N' option to
turn off structured comments (such as `%%Page').  Otherwise, programs
that read your file will assume its pages are independent.