How does the browser know that a page is HTML?

• HTTP Message includes a Multipurpose Internet Mail Extension (MIME) Type to indicate what is being transmitted.
• Browser sniffs the file
• Browser looks at file extension
• Browser looks at <meta> elements (unlikely)

Possible MIME Types transmitted are:

• text/html: for HTML files but works for XHTML 1.0 and XHTML 1.1 as well
  • In theory, these files will not be processed as XHTML
  • Strictly, XHTML 1.1 should not be served as text/html but XHTML 1.0 can
  • Not well formed documents will be accepted
• application/xhtml+xml: the media type that should be used
• application/xml: generic media type for XML applications, need to add the XML namespace as XHTML
• text/xml: almost equivalent to application/xml