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:
Public Identifier: "-//W3C//DTD HTML 4.01 Transitional//EN"
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.