[2] Web Applications 1.0 r7452 Allow 'opacity' and 'visibility' on ::cue ( ( 版)) <http://html5.org/tools/web-apps-tracker?from=7451&to=7452>
[3] Chromium Blog: Chrome 25 Beta: Content Security Policy and Shadow DOM ( ( 版)) <http://blog.chromium.org/2013/01/content-security-policy-and-shadow-dom.html>
[4] WebVTT: The Web Video Text Tracks Format ( ( 版)) <http://dev.w3.org/html5/webvtt/#the-cue-pseudo-element>
:not()
や:match()
と同じように計算するべきな気はします。