Anchor the alternation in the :link and :placeholder-shown tests

[jdalton]

/^a|area$/ alternates ^a with area$ rather than anchoring an alternation, so :link and :any-link match any element whose name begins with a, <abbr href> among them. /^input|textarea$/ in :placeholder-shown has the same shape.

Detail, and how it was checked

/^a|area$/ reads as ^a or area$, so it accepts any element whose name begins with a. :link and :any-link therefore match <abbr href="...">, where browsers match only <a> and <area>. It agrees with browsers on those two, which is why the test suites do not catch it.

/^input|textarea$/ in :placeholder-shown has the same shape; there the surrounding conditions happen to mask it.

The link test is hoisted into a helper at the same time, so the three places that need it share one definition.

Extracted from #167 as a standalone change: one file, applies to master on its own, and checked against a fixture to confirm it fixes what it describes and moves nothing else.

References: the spec, the browser source, and what each part was reasoned from

This patch applies to master on its own. The sixteen in this series were checked by cherry-picking them onto master one after another, in this order and in reverse, and all sixteen land without a conflict.

• Spec: the any link pseudo — :any-link matches an a or area element with an href.
• Spec: selector placeholder shown — :placeholder-shown, for the pattern of the same shape.
• Chromium: selector_checker.cc#L2550 — :any-link is one IsLink() predicate.
• Chromium: selector_checker.cc#L2553 — :link is the same predicate, unvisited.
• MDN: :any-link.

[jdalton]

This one sits with #179 and #180, which touch the parser and pattern fixes.

They do not depend on each other. All seventeen in the series cherry-pick onto master in any order, and I checked that in both directions, so any one of these can land alone. The order below is the one they read best in:

• #179 fixes the forgiving fallback and the EOF-terminated argument.
• #180 lets a pseudo-class be followed by a quoted attribute selector.
• #181 anchors the alternation in the :link and :placeholder-shown tests.