Click the MaskDefinitions node in the Application options to open the following screen:

From here, you can set the characters that are allowed to be used for creating the mask of a Maskeditbox.
In the Definitions memo box the mask definitions can be created, one definition on each line.
The format is: x:yyyy
The Character memo box displays the mask character of the selected entry in the definitions.
The Range memo box displays the range of characters of the selected entry in the definitions. This entry changes dynamically while you edit the selected mask definition.