There are some authors that write every few weeks a new program or a new hypertext. And in every documentation you can read a disclaimer or a copyright chapter. Wouldn't it be easier to use the same text all the time?
No problem, just use macros. The following example shows how to use a standardized copyright text. May be you have a written a program that contains this copyright note:
""Hello, World!"" Version 8.15 (!nl) Copyright (!copyright) 1996 by C. Rookie
Your next program contains a similar text, only the name of the program and the version number differ. Wouldn't it be better to use a standardized text any time you write the documentation of a new software?
""(!PrgName)"" Version (!PrgVersion) (!nl) Copyright (!copyright) (!PrgYear) by C. Rookie
Here the name, the version number and the years will be replaced
by the contents of macros
PrgYear. If you write the upper text to a sinlge file you can
use it for many documentations where only the macros have to be
!macro PrgName Hello, World! !macro PrgVersion 8.15 !macro PrgYear 1996 ... !begin_document ... !include copyleft.ui
Surely this is only a small example. But you can make more complex files if you want to.