[1] Styling – SVG 1.1 (Second Edition) ( ( 版)) <http://www.w3.org/TR/2011/REC-SVG11-20110816/styling.html#AuralStyleSheets>
[2] [css-speech] Rename 'speak: none' and 'speak: normal' to 'speak: neve… (fantasai著, ) <https://github.com/w3c/csswg-drafts/commit/4acaaa71fa965e55f0c175371e96532473f098cb>