2.1.3 [DOM Level 2 - Style] Section 1.4, Association between a style sheet and a document.
The underlying style sheet will be created after the element is inserted into the document and the type attribute is set in a way indicating that the element corresponds to a style sheet language interpreted by the user agent.
Quirks Mode, IE7 Mode, and IE8 Mode (All Versions)
Inserting a style sheet by creating a new STYLE element is supported, but rules can be edited only through the Rules collection of a styleSheet object.
HTML and Style Sheet Removal Removing a LINK HTML element or a STYLE HTML element removes the underlying style sheet from the style sheet collection associated with a document. Specifically, the removed style sheet is no longer applied to the presentation of the document.
All Document Modes (Internet Explorer 7)
When removing a LINK element or a STYLE element from a document object through a script, the underlying styleSheet is removed from the style sheet collection associated with a document (document.styleSheets). However, the style is still applied to the presentation of the document.