Link validation issue on TinyMCE using Classic Editor

[audrasjb]

Just spotted a small issue on Classic Editor, during the 5.6.2 release party.
New links seem to have a data-wplink-url-error="true" attribute after they are inserted. It’s ok after the post is saved.

[sabernhardt]

I think the error showed because the URL includes localhost (see ticket:36638#comment:47). I get the same error on my local installations.

The link validates positively when I try selecting a page on a site with public URLs, though.

[sabernhardt]

@azaozz mentioned that localhost links 'should never appear on a "live" web page', but maybe it could be worth ignoring them in the ​checkLink() function.

if ( /^http/i.test( href ) && ( ! urlRegex1.test( href ) || ! urlRegex2.test( href ) ) && ( ! href.includes( '://localhost' ) ) ) {