Be explicit about fallback roles being unsupported

[WilcoFiers]

Currently, when you do something like this:

<div role="application tablist">

Axe-core reports "ARIA role is valid". That's a confusing message. Instead it should say something like "Use only one role value, since fallback roles are not widely supported".

Proposal on how to do this

1. support fallback roles in the existing *role tools, have them look at each role in the role="" attribute
2. Add a new check that looks just for use of fallback roles

That way something like role="foobar textbox select" would be reported as:

Fix all of the following:
- Use only one role value, since fallback roles are not widely supported"
- Abstract role 'select' cannot be directly used
- Role 'foobar' must be a valid ARIA roles

We'd have to update the message to indicate which role is invalid / abstract, and report multiples. (e.g. "abstract roles 'select', and 'landmark' cannot be directly used".

[jnurthen]

Fallback roles are pretty well supported except on IE. For those of us writing products which don't support IE is there any chance we could have a way of allowing fallback roles.
I'm trying to write a meter right now and am using role="meter progressbar" causing aXe errors

[WilcoFiers]

Getting axe-core to run entirely with support for fallback roles is going to take a while. But I'm pretty confident some time next year this will change. This change will be the first step, by creating a separate check for this, it also makes it possible to turn the check off, separate from the rest of the rule.

I also think it's still worth pointing out that IE still makes up 15% of the WebAIM survey market. That's a significant enough portion that I'm comfortable saying we should flag it for a while still.

[jeankaplansky]

Release notes updated 2/04/2020

[padmavemulapati]

Instead Aria-role is valid, if displayed some non-confusing accessible name could be better , verified with aria-role.html rule test file,