If you use RCS or CVS to maintain your (La)TeX documents under version control, you may need some mechanism for including the RCS keywords in your document, in such a way that they can be typeset (that is, rather than just hiding them inside a comment).
The most complete solution is to use the (LaTeX) package rcs, which allows you to parse and display the contents of RCS keyword fields in an extremely flexible way.
If you need a solution which works without using external packages, or which will work in plain TeX, then you can use the following quick (but usually adequate) hack:
\def\RCS$#1: #2 ${\expandafter\def\csname RCS#1\endcsname{#2}}
\RCS$Revision: 1.96 $ % or any RCS keyword
\RCS$Date: 2002/09/05 11:57:40 $
...
\date{Revision \RCSRevision, \RCSDate}