JESS: Rule firing during execution of RHS

Hi,

Execution of a rule RHS is sequential. But is it atomic?
In other words, during that time, is it possible that other activated
rules get fired?
These activated rules include those that had been on the agenda or newly
activated rules due to pattern matching caused by the RHS invocation of
modify, assert or retract.

Any feedback is greately appreciated.

Son Nguyen