I have written code to validate data based on Chapter 10 Exercise 1[pages 
384-385] from the book.  The validation takes place in a subroutine that 
runs when a button is clicked.  My problem is that when a user uses the 
enter key rather then the submit button the subroutine gets skipped.  I 
noticed that the Chapter 10 Exercise 1 page has some how disabled the 
enter key.  This forces the user to use the button.  How do you do that?