TextInput control

[JoeDeveloper]

I have a TextInput box for a user to enter a number of the format XXXX.XXX

The user enters both the decimal point and the numbers (0-9). The largest the number can get is 9999.999. Is there any way in which I can put a restriction on this TextInput box for the parameters I listed above (users can't enter more than four numbers before the decimal point and no more than three numbers after inputting a decimal point)?

I've tried manipulating a few things (ie, restrict, maxChars, etc) but I can't find anything that works. I am stuck between a rock and a hard place.

Other ideas are welcomed as long as I get the format above!

Thanks