Revisit our legacy browser support

[vanitabarrett]

What

We should revisit our level of support for older browsers (e.g: IE11). This work may help us inform some of the JavaScript work (#1389), e.g:

• polyfills
• newer features we currently avoid to support older browsers
• tooling choices

Why

It seems likely that the Service Manual may update the support for IE11 in the next year or so (e.g: removing or updating to 'functional' support). While we follow the Service Manual, we also know that roughly 40% of services that filled in the Government Frontend Survey 2021 still support IE11 (various reasons being: supporting staff/internal/legacy systems; high percentage of their users still use IE). At the moment, we support more browsers than those listed in the Service Manual, so we can set our level of support ourselves as long as we still meet the minimum required by the Service Manual.

Who needs to work on this

Developers; Tech Writer

Done when

• Gather together data and research to inform decision on legacy browsers #2517
• Write and share a proposal for our browser support #2519
• [parked] Investigate what supporting service teams who have different browser requirements to us might look like #2518

[vanitabarrett]

Follow-up epic: #2621