http://docs.jboss.org/drools/release/6.1.0.Beta2/drools-docs/html_single/
Search for "modify" after "7.8.3.7.2. Conditional Element from",
where
examples contain lines such as
modify ($p) {} // Assign person to sales region 1 in a modify block
which is bound to cause confusion. These omissions continue until
"7.8.3.7.3. Conditional Element collect".
-W