To only allow numerical data for a Multiple Textboxes question: If you add an "Other" textbox to a close-ended Multiple Choice, Dropdown, or Matrix question, you can validate that field to require respondents to enter their answer in a specific format.None of the solutions above are error free or really safe cross-browsers.Text fields and text views have two main functions: to display text and to enable the entry and editing of text.Several programming tasks are associated with these simple purposes, including configuring the text object, accessing the current text, validating what the user enters, and displaying overlay views such as bookmark buttons in text fields. When the user taps a text object, it automatically becomes first responder; as a result, the system displays the keyboard and an editing session begins for that text object.
You can configure them either programmatically or using the attribute inspector of Interface Builder. If there is only one text object in the currently displayed view, the identity of the text object referenced by the parameter is obvious.
So I'm leaving the question open for some more time...
It attempts to only let the user enter valid numbers, but since this is impossible (while the user is still typing, the value will be invalid), it also accept valid prefixes (showing a red border if the whole text is not valid).
This article explains how to use validation rules and validation text in table fields and form controls.
A validation rule is one way to restrict input in a table field or a control (such as a text box) on a form.