Hi,
To apply a mask and other textbox settings to the "other" option, first create a <textbox> element with the appropriate caption and mask, and then specify that textbox as the other option (that's right, you can specify the name of a textbox to be the other option).
For example:
<textbox otheroption>
/ caption = "other"
/ mask = positiveinteger
</textbox>
<radiobuttons numbers>
/ caption = "What is your favorite number"
/ options = ("1", "2", "3", "4")
/ other = otheroption
</radiobuttons>