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A vertical position trap calls a macro when the formatter’s vertical drawing position reaches or passes, in the downward direction, a certain location on the output page or in a diversion. Its applications include setting page headers and footers, body text in multiple columns, and footnotes.
Enable or disable vertical position traps per Boolean expression
b. They are enabled by default, and if b is omitted.
Vertical position traps are those set by the wh
request or by
dt
within a diversion. Vertical position trap enablement is
global. Its status is stored in the .vpt
read-only register.
A page can’t be ejected if vpt
is set to zero; see The Implicit Page Trap.
• Page Location Traps | ||
• The Implicit Page Trap | ||
• Diversion Traps |