Besides, this approach is really handy on mobile devices. We can use only numeric keyboard for the first 3 fields without the need to force a respondent to switch between alphabetical and numeric keyboards all the time.
Checkout Form: Behind The Scene. p2
Dmitry Kovalenko

Can’t you also default the keyboard layout to what can be entered? Eg paypal have underscore and other characters on the email input field mobile keyboard.

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