Hi! I did this UDF for me (and you ). It tests while typing if the text entered to an input filed (should work with edit too) is atm fitting into a given RegExp or if it still can fullfill it. How to use: To start it up, you use: _RegEx_RestrictControl_setup (20) ; prepare for up to 20 Controls to restrictoÝ÷ Ù'­¶)àj·¬¶¸¶*'¢v¢{k¢X¬vÞjdz&¬¶¬jëh×6$inp = GUICtrlCreateInput("", 10, 10, 100, 20) _RegEx_RestrictControl_add ($inp, "^[a-z]{0,10}$") ; up to 10 letters $inp2 = GUICtrlCreateI