changes to address #517

[awkawk]

changes to the Understanding document to address the issue.

[alastc]

That solves the issue raised, I wonder if we need to tackle the issues about contrasting between states?

I've been asked if link-states need to contrast with each other (and the background), or just against the background.

My reply was that it is against adjacent colors, so a link's contrast is not against itself, perhaps add something like:
"...Also, any visual effects implemented which are necessary to indicate state, such as whether a component is selected or focused, must also ensure that the information used to identify the control in that state has a minimum 3:1 contrast ratio. Added: The state indicators are not required to contrast with each other. For example, a text link which changes from blue to purple when in a visited state has to contrast with the background, not un-visited state."

[awkawk]

@alastc Let's resolve the issue at hand and then deal with further changes as needed.

[alastc]

Approved here: https://www.w3.org/2018/11/20-ag-minutes.html#item06