Form validation that requires 4 characters

eg.

^[a-zA-Z0-9]{4}$‍‍

(allows both lower- and upper-case characters and any of their mix. if you only want lower-case ones remove 'A-Z' from the pattern)

Works perfect.  Thank you.

I need for the submittere to enter the year in to a text box. 

I tried use the script but I only need 4 number, so I removed "a-zA-Z".  

I still get an error message.  Need help not sure what I am doing wrong.

Thanks

Thank you Simon it works!! 

 I went back and had to delete the single text box field and crate a new one.  Instead of coping and pasting the expression I typed it in. 

Thank you Simon it works perfect! Thank you.

happy wheels