<Applet code="ApplicationClassName/ObjectID " param="parametername" [valuePatterns="" source="*"] />
where
code is the name of the applet or object class (mandatory)
param is the name of the parameter whose value needs to be rewritten (mandatory)
valuePatterns See Using Pattern Matching in Rules.
source is the URL of the page that contains the applet definition (optional, default is *, meaning, in any page)