Your regex validator should run automatically (on the client side) whenever a command control is triggered.
If you want to run the validation manually from a script, you could use the validate method from the CAF model.
See:
http://techcommunity.softwareag.com/ecosystem/documentation/webmethods/wmsuites/wmsuite8-2_sp2/My_webMethods/8-2-SP1_CAF_JavaScript_Reference/CAF.Input.Model.html#validate
For example, something like this in a script block control:
var m = CAF.model('#{caf:cid("input_control_id_here")}');
var msg = m.validate(true);
if (msg == "") {
//input was valid
} else {
//input was not valid. the msg variable contains the reason.
}
#webMethods-BPMS#webMethods#MWS-CAF-Task-Engine