index.html does not validate

[moloko]

if validated using https://validator.w3.org/, two errors and a smattering of warnings are shown

[oliverfoster]

What are we validating against? This has to be part html4, part html5, part iOS + IE hacks.

[moloko]

I'm just chucking src/index.html in to the above validator, nothing more...

[moloko]

for example it highlighted that the accessibility button had role='button' which is obviously not needed - assume it was just from when we used to use anchor tags for things like this

[oliverfoster]

Yea, that's fair.

[moloko]

see #998

I'll also need to do the files in contrib-spoor; will do that once this is accepted