The LHS wildcard operators ($*, $+, $-, and $@) and the LHS class-matching operators ($= and $~) can have their matched values copied to the RHS by the $digit positional operator. Consider, for example, the following rule:

R $+ < @ $- . $* >        $: $1

Here, there are three wildcard operators in the LHS. The first (the $+) corresponds to the $1 on the RHS. The object of this rule is to match a focused address and rewrite it as the username. For example, gw@wash.dc.gov will be rewritten to be gw.

The $digit operator can be used only on the RHS of rules. See Section 18.7.1 in this chapter for a full description of this $digit operator.