How do you make a textbox to only accept letters (no numbers and special characters)?

Hello, i want to make my textboxes accepts letters only from A-Z no numbers and any special characters.

This will remove the last character in the textbox if it is not a letter:

It gets more complicated if the user enters a non letter in the middle of text, you have to be careful to avoid an infinite loop when iterating over each letter, and you work backwards to preserve the indexing of earlier letters in the list:

note: I add a space to the letters list on screen Initialise (it doesn't convert with csv row to list)

Textbox_azAZ.aia (10.9 KB)

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To also allow spaces and remove non-AZ characters in the middle of the text: