<style>is CDATA in HTML
To make it easier to author documents in plain text, HTML process
<style> as CDATA
<!ENTITY % Script "CDATA" -- script expression --> <!ENTITY % StyleSheet "CDATA" -- style sheet data -->
— HTML 4.01 Strict DTD
This makes it impossible to serialize text containing end tag, try it yourself:
What you load differs from what you've saved. This breaks live authoring. Fixed in XHTML.