The procedure is exactly the same as for the two previous handlers, but the validation code is different because occupation must be Programmer or an empty string to be valid. The ASCII values for the characters between 0 and 9 lie between 48 and 57, so you make sure that the character is within this range. The ASCII value 8 is the Backspace key, and for editing reasons, you allow this to slip through.
Setting the tells the control that it shouldn't do anything else with the character, and so if the key pressed isn't a digit or a backspace, it is not shown.
Available new tools for specification of dimensions and geometrical tolerances are discussed.
Text boxes should be used when you want users to enter text that you have no knowledge of at design time (for example, the user's name).
An example of this is when a user clicks a Help button.