See: http://lists.w3.org/Archives/Public/public-html/2012Nov/0049

DESCRIPTION: 

   (1) The introduction contains this code:
       <dfn id="dfn-polyglot-markup">polyglot markup</dfn>.
   (2) Every time the spec uses the term "polyglot markup",
       then it points to #dfn-polyglot-markup.
   (3) But Smylers pointed out that it perhaps is illogical
       that the definition of "polyglot markup" is kept in
       a section that bears the stamp "This section is
       non-normative". 

HOW TO FIX:

EITHER: Remove the "non-normative" stamp.

    OR: Regardless of the normativity of the 'Introduction',
        create a new header called e.g. 

       'The polylglot markup syntax', 

        and insert <dfn id="syntax">polyglot markup</dfin> 
        in that section, and and point to *that* section
        when referring to a definition of "polyglot markup".
 
        I would also move the currenct section 2 until section 10
        under the new header - under a subheader called
        "Writing polyglot HTML documents"

        All, in all, the document structure of the Polyglot 
        spec, would now look as follows:

1. Introduction
2. The polyglot HTML syntax [New]
   [definition of polyglot syntax goes here]
   [May be one could also include a reference 
    to HTML5’s 2 syntaxes here, see below.]

2.1 Writing polyglot HTML documents [New]

       [Current section 2 to 10: ]
2.1.2. Processing Instructions and the XML Declaration [… snip …]
2.1.10. Comments in Polyglot Markup
3. Example Document


JUSTIFICATION for the AND/OR variant - which is what I think I prefer:

  The AND/OR otion is inspired by HTML5 itself, 
  which operates with 2 syntaxes:

 HTML: http://dev.w3.org/html5/spec/syntax.html#syntax
XHTML: http://dev.w3.org/html5/spec/the-xhtml-syntax#the-xhtml-syntax

  And often when HTML5 refers to "HTML" or XML, then it
  points to the above syntax sections.

  Polyglot Markup is a specific third, hybrid syntax. And thus, the
  proposed, new structure follows, a littl bit, the structure found
  in HTML5's HTML syntax section 
  (http://dev.w3.org/html5/spec/syntax.html#syntax)

  There is a great attention to the fact that Polyglot Markup is
  "just" the hybrid of the XHTML syntax and the HTML syntax. May
  be these changes could underline that fact.