Consider removing the pattern attribute from date input once traffic from iOS < 12.2+ drops off

[36degrees]

What

We use the pattern attribute to force the inputs within the date input component to trigger a numeric keypad on iOS < 12.2+, (and possibly some older Android browsers?)

Why

Once the number of users that require the pattern attribute in order to trigger a numeric keypad has dropped to a low enough percentage, we can remove it and rely exclusively on inputmode.

[36degrees]

iOS < 12.2 accounted for 1.37% of all iOS traffic in May 2021 – or 0.43% of all traffic – with 91.49% of iOS users running iOS 14.

[querkmachine]

In March 2022, iOS versions 12.2 and below accounted for around 0.19% of iOS traffic and 0.08% of total traffic on GOV.UK.

[querkmachine]

Reasons to remove it:

• It's largely redundant now that inputmode is supported by the vast majority of visitor's devices.
• Having unnecessary code and tests in Frontend is undesirable from a maintenance perspective.
• We're sending a few extra bytes down the wire where it probably isn't necessary.

Reasons to keep it:

• It provides a better experience for the small number of users who still benefit from it.
• The pattern attribute has client-side validation benefits (though I'm not sure if any services use it in this way).

Other notes:

• As far as I can tell, the presence of inputmode or pattern doesn't change how the fields are announced by screen readers, nor limits what can be entered by voice control or dictation.

[36degrees]

• The pattern attribute has client-side validation benefits (though I'm not sure if any services use it in this way).

We currently tell people to turn off client-side (HTML5) validation, although it's a bit buried.

I think this might if anything be a reason to remove it. If service teams don't turn off HTML5 validation then this is one of the few attributes we use across the codebase which would trigger client-side validation, which isn't always that accessible or helpful ('Please match the requested format.')

On balance, I'd support removing it at this point 👍🏻