Compile time error thrown when the code contains a call to a private method that isn't defined in the current class, and when no appropriate trusts relation is defined that permits the private method call.
===SORRY!===Cannot call private method 'foo' on because it does not trust GLOBAL
method method(--> Str)
The name of the private method
method source-package(--> Mu)
Returns the type object that (supposedly) contains the private method.
method calling-package(--> Mu)
Returns the package in which the calling code is, and which the source package does not trust.