When viewing my page in Firefox page source, I am getting the first line in red italic:

What is causing this and is it an issue?

1 Answer 1


If you mouse over the doctype you'll see that Firefox is rendering the page in "Almost standard mode".

The DOCTYPEs that will trigger "almost standards" mode are those which contain:

  • The public identifier "-//W3C//DTD XHTML 1.0 Transitional//EN"
  • The public identifier "-//W3C//DTD XHTML 1.0 Frameset//EN"
  • The public identifier "-//W3C//DTD HTML 4.01 Transitional//EN", with a system identifier
  • The public identifier "-//W3C//DTD HTML 4.01 Frameset//EN", with a system identifier
  • The IBM system DOCTYPE "http://www.ibm.com/data/dtd/v11/ibmxhtml1-transitional.dtd"

A complete DOCTYPE contains a public identifier and a system identifier. In discussions of DOCTYPEs, many people will refer to a DOCTYPE as being "with URI" or "without URI." The URI is the system identifier. For example, consider the following DOCTYPE:

 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> The parts are as follows:

Thus any HTML 4.01 Transitional or Frameset DOCTYPE with a URI (system identifier) will trigger "almost standards" mode, as will any XHTML 1.0 Transitional or Frameset DOCTYPE, with or without the URI. Authors outside of IBM do not need to worry about the custom DOCTYPE that will also trigger "almost standards" mode.

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