Using a variable on the left of 'matches' fails in 6.2.0.FInal, when it worked in 6.1.0.Final. E.g.

when
Fact( $field : field )
RegEx( $field matches pattern )

results in
[Error: unable to resolve method: defaultpkg.RegEx.$field() [arglength=0]]
[Near :

]

This can be worked around for the positive case by simply moving the constraint, e.g.

when
RegEx( $pattern : pattern )
Fact( field matches $pattern )

But it makes it impossible to find facts that are not matched by any regex, e.g.

when
Fact( $field : field )
not RegEx( $field matches pattern )