The masking pattern used when data is input into the entry field.
A 256-character string, defining an input mask for the field.
The input mask is applied only when the form field is available (unprotected) and has focus.
When the field loses focus, the input mask disappears; if a display mask (DataMask ) is available, that mask is then applied.
For a more detailed explanation of mask patterns and their relation to data types, see Masking.