Just like classes, rules allow inheritance between them. If rule B inherits rule A, it will be the same as having all the conditions in rule A at the beginning of the conditions of rule B. Consider:

rule "A"
when
  s: String(this == "A")
then
  ...
end

rule "B" extends "A"
when
  i: Integer(intValue > 2)
then
  ...
end

Is same as:

rule "B"
when
  s: String(this == "A")
  i: Integer(intValue > 2)
then
  ...
end