There is a range of
"Standard Definitions"
available for use in your source. You can create your own as well
(for example a formatted date/time of your document).
You can selectively include or exclude portions of the source
code using the "#if" command.
Large portions of text (with or without HTML tagging) that you place in
multiple places which you feel must be kept in sync
can be defined once with "#define" and referenced many
times.