Principles that put the "Extreme" in ExtremeProgramming.
These are applied to ExtremeValues to effect ContinuousCommunication and ContinuousSimplicity, which together achieve the goal of XP to EmbraceChangeContinuously.
The number of software development patterns or strategies and principles of the form "do <
You can think of "proactivity" as the "early" part, and "frequency" as the "often." The way XP differs from what might be considered more traditional IterativeAndIncrementalDevelopment methodologies is that it does things extremely early and extremely often. Hence ExtremeProactivity and ExtremeFrequency.