All system functions were removed from version 2.0 of Web Rule. Thanks for your feedback! The source code of all those functions can be found here
Originally, system functions have been designed to add some convenience for developers. For example, instead of writing your own function that verifies if some field contains a valid email address you could use the system function called IsEmail(). There are 18 such functions built into Web Rule; their names are listed in the CodeEffects.Rule.Common.SystemMethod enumerator.
The problem is that they are quite different from in-rule methods and actions. Supporting them adds a lot of extra complexity to Web Rule's code base. But we don't really see our customers using them. The related documentation pages on our site have almost no traffic and no one asks questions about them or sends any kind of feedback or support requests.
The question is: do you use them?
Should we continue to support them? Or should we just dump the whole thing for the sake of simplification of Web Rule?
These system functions are integrated into Web Rule in a very deep level and we cannot just "deprecate" them as we did with AspControl class in version 2.0, for example. So, it's either all or nothing. Pretty much...
On the up side, the internals of Web Rule would be simpler if we'd completely remove them all and move on. Simpler is always a good thing.
On the down side, if you use any of them in your rules, those rules will start throwing exceptions. And there is no programmatic cure for that - you will have to code the functionality that they used to provide and manually change XML of your rules or recreate them all over again.
So, do you use these system functions? Please comment.