2.2.9 [XML] Section 3.2.1, Element Content


The specification states:

 Validity constraint: Proper Group/PE Nesting
 Parameter-entity replacement text MUST be properly nested with parenthesized 
 groups. That is to say, if either of the opening or closing parentheses in a 
 choice, seq, or Mixed construct is contained in the replacement text for a 
 parameter entity, both MUST be contained in the same replacement text.
 For interoperability, if a parameter-entity reference appears in a choice, seq, or 
 Mixed construct, its replacement text SHOULD contain at least one non-blank 
 character, and neither the first nor last non-blank character of the replacement 
 text SHOULD be a connector (| or ,).


The following clarifications apply:

  • Parameter-entity replacement text can be blank if it is valid as defined in the DTD.

  • Parameter-entity replacement text can have the characters '|' or ',' at the beginning or end of the string if it is valid as defined in the DTD.