This ruleset based language describes user preferences so that user agents can "make automated or semi-automated decisions regarding the acceptability of machine-readable privacy policies from P3P enabled Web sites."

APPEL complements the P3P 1.0 working draft released earlier this month and updates the much earlier P3P Preferences draft of August 1998.

The draft describes the expected usage for the language :

"Primarily, we envision this language will be used to allow users to import preference rulesets created by other parties and to transport their own rulesets files between multiple user agents. User agent implementors might also choose to use this language (or some easily-derived variation) to encode user preferences for use by the rule evaluators that serve as the decision-making components of their user agents."

The ordered ruleset concept on which APPEL is constructed defines an algorithm to "match expressions against available evidence" relying on simple regular expressions which differ "from its semantics in standard regular expression systems such as egrep".