Strange question about variables?

I'm working on a PHP editor and I am trying to make a syntax check and I thought it would be nice to beging to check if all variables are correcly written and therefore I wounder if any one of you would like to tell me the best way of checking this. I've made a check on the first letter in the variable so it isn't a number. But then we are about to check de rest and see so there isn't any "{" or any "/" in the middle of the variable. Is there a range or asci that I can use to find illegal characters in a variable? like: if (variable >= 120 and variable <= 200) then error end if I don't know if you want to help me with this but I'l give it a try. BTW, the editor is for Mac right now, but may be translated for PC (Windowz) later on, if I got the time... If there allready is a good PHP editor for Mac/PC, let me know. Thanks /Magnus Hammar --------------