Allow checking contrast at AAA level with contrast-checker

[danielck]

What problem does this address?

The current contrast-checker component in core uses the tinycolor library to check the contrast between two colour values. The specific isReadable method used by contrast-checker supports both level AA and AAA, but currently level AA is hard-coded into the WP component:

		tinycolor.isReadable( tinyBackgroundColor, tinyTextColor, {
			level: 'AA',
			size:
				isLargeText || ( isLargeText !== false && fontSize >= 24 )
					? 'large'
					: 'small',
		} )

This means that for site owners or developers wishing to enforce criterion 1.4.6 Contrast (enhanced), doing so would require developing a custom component.

What is your proposed solution?

Level AA is a very good default and I do not propose changing this. However, adding a JS or PHP filter for the level would at least allow developers to change the level relatively easily.

[aristath]

Nice suggestion. Marked as a feature-request for the color-contrast checker 👍