Parameter entity reference error with expat

David Megginson david at
Wed Jul 15 03:14:25 BST 1998

Steve Harris writes:

 > I'm working out a small DTD by inlining it with some sample data. It
 > uses a single internal parameter entity and refers to the entity twice
 > in the DTD. Emacs's 'psgml' seems to validate and do all the
 > substitutions as expected. If I run the file through expat, though, it
 > reports the following error:
 > 	illegal parameter entity reference

You've run up against a somewhat obscure constraint from section 2.8
of the XML 1.0 Recommendation:

  Well-Formedness Constraint: PEs in Internal Subset

  In the internal DTD subset, parameter-entity references can occur
  only where markup declarations can occur, not within markup
  declarations. (This does not apply to references that occur in
  external parameter entities or to the external subset.)


As a result, the following is legal in an _external_ DTD subset, but
not in an internal one:

  <!ENTITY % my-atts "id ID #REQUIRED
                      role CDATA #IMPLIED">

  <!ELEMENT foo (#PCDATA)>
  <!ATTLIST foo

PSGML doesn't catch this one yet.

All the best,


David Megginson                 david at

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