Embedding CSS styles into the HTML elements of a web document is allowed by the HTML5 specifications, provided that you use the
scoped attribute of the style element. This feature has interesting implementations for some popular CMS frameworks
(such as WordPress) where many widgets and plugins make a large use of this kind of embedded styles.
Just a word of caution: if you're developing a widget or a plugin, you can't know in advance which kind of DTD will be used. This feature is valid in HTML5 only, so be cautious.
