These are place holders for the introduction of style sheets and client-side scripts in future versions of HTML. User agents should hide the contents of these elements.
These elements are defined with CDATA as the content type. As a result they may contain only SGML characters. All markup characters or delimiters are ignored and passed as data to the application, except for ETAGO ("</") delimiters followed immediately by a name character [a-zA-Z]. This means that the element's end-tag (or that of an element in which it is nested) is recognized, while an error occurs if the ETAGO is invalid.