The RegEx engine of Javascript and VBScript lacks some advance features, though Easy GREP can accept some of them but most of them can't be implemented,
Supported but different from some other RegEx engine
Not supported
To be compatwith these advanced RegEx grammar, Easy GREP simulates some of them.
Such as "dot match all", it actually convert dot to (.|\n) before execution, as well as filter (?:X) to (X). So these two syntax are supported in input and work, but the speed will not improved if you write (?:X) instead of (X). And you cannot apply them to Javascript and VBscript in your program.
If you think Easy GREP can't satisfy your demand you can choose a more powerful tool, we recommend PowerGREP by Just Great Software (by Jan Goyvaerts) which is respectable.