In the TemplateGrid the same widgets can be used as for the Dataview. This means that a textbox also has the inputmask property. The inputmask property defines what kind of input is accepted in the input (see the documentation in the Modeler).
However, a TemplateGrid is always readonly, this means that you can not edit data using a TemplateGrid. Hence, setting the inputmask property on a textbox in a TemplateGrid does not have any effect.
Input mask can be used to limit the kind of inputs the user can type in an input field.
For instance, '999999' wil limit the input of the user to numbers, it will not be allowed to type in alpha-numeric characters.
Other examples are documented in the modeler, if you click on the 'input mask' property, documentation will appear between the properties box and the connector
I just saw the documentation in the modeler (which I wasn't aware of...):
"The input mask limits what the user can enter in the text box. A '9' means any digit, 'Z' means any letter, 'U' an upper-case, 'L' a lower-case letter and '*' a letter or a digit. Other characters will be taken literally. For example, the input mask 99-LLL-9999 matches 24-apr-2008."