There is no universal answer to how a widget should react to a user trying to enter bad data. The validation logic found in various graphics toolkits can differ greatly; when bad data is entered, an input widget might validate the user input as follows:
- Prevent the invalid keystrokes from registering at all
- Accept the input, but return an error or list of errors when the form is submitted
- Show an error when the user leaves the entry field, perhaps disabling form submission until it's corrected
- Lock the user in the entry field until valid data is entered
- Silently correct the bad data using a best-guess algorithm
The correct behavior in a data entry form (which is filled out hundreds of times a day by users ...
