It is often valuable to group rule sets by function and call them as subroutines from a rule. To illustrate, consider the following rule:

R $+ < @ $+ >           $: $>set

Here, the RHS $>set operator tells sendmail to perform additional rewriting using a secondary set of rules called set. The workspace is passed as is to that secondary rule set, and the result of the rewriting by that secondary rule set becomes the new workspace.

The $> operator is described in full in Section 18.7.4.