Browser portability

[ben-sagar]

This may have been entirely superseded by Government guidance, but was originally written within the context of Defra delivery so there may be the odd bit of information that can be harvested.

[nigejohnson]

Again I've no opinion as to where the content should ultimately live, but most of the content seemed fine. My only quibbles with the content would be that I was unclear what is being said about progressive web applications (PWAs).
I'm also not sure to what extent it is worth saying anything about mobile applications standards here. Certainly I would agree with the GDS recommendation that progressive web applications are to be preferred to mobile applications where at all possible, as the skills involved are more transferable and much more likely to have a longer shelf life (so time and money invested in learning will have a bigger pay-off) and because costs of ownership are likely to be much lower. It might be worth referencing that recommendation here.
Of course, sometimes we will still have to build mobile apps, especially as our preferred devices are Apple and Apple only grudgingly support progressive features in Safari/Webkit (and force all browsers on their devices to actually use Webkit under the covers!) in an effort to preserve their monopolistic business model (though it is still possible to create a perfectly useful PWA for an Apple device, even if you can't do the fancier things like actually install it as an app on the home screen!).
So possibly we do need to start something on mobile standards too, but I'd keep that separate, especially as the Cordova-style "run the mobile app in a hidden browser engine" approach is now falling rapidly out of favour, partly because of the ever stricter enforcement of "single origin" (and a mobile app rendering local content automatically uses up one origin before it even starts to interact with any "remote" systems!) but also because the newer frameworks such as Facebook backed React and Google backed Flutter no longer use this approach. Therefore, in the future, there is going to be even less overlap between browser considerations and mobile app development, as even "cross platform) mobile apps will make much less use of browser engines (and usually none at all).

[irisfaraway]

If we think some of this may have been superseded by government guidance elsewhere, I think it'd be good to look into that before we merge this. Then we can remove any duplication and link to the relevant guidance where it exists.