You can allow certain characters that can be entered in the textbox for letters only or numbers only. This is very useful in entering a particular format, for example such as inputting a phone number.
Return: True if successful
Where acceptable are macros that can be seen here.
textboxUsername = ui_textbox_create(32, 24, 128, ui_default, "Username"); ui_textbox_set_acceptable(TextboxUsername, ui_number_only);
The above line of code is used to change the textboxUsername textbox only accept input for numbers only.