XML in a Nutshell, 3rd Edition

Parameter Entity References for Namespace Prefixes

Requiring DTDs to declare the prefixed names, instead of the raw names or some combination of local part and namespace URI, makes it difficult to change the prefix in valid documents. The problem is that changing the prefix requires changing all declarations that use that prefix in the DTD. However, with a little forethought, parameter entity references can alleviate the pain quite a bit.

The trick is to define both the namespace prefix and the colon that separates the prefix from the local name as parameter entities, like this:

<!ENTITY % dc-prefix "dc">
<!ENTITY % dc-colon ":">

The second step is to define the qualified names as more parameter entity references, like these:

<!ENTITY % dc-title       "%dc-prefix;%dc-colon;title">
<!ENTITY % dc-creator     "%dc-prefix;%dc-colon;creator">
<!ENTITY % dc-description "%dc-prefix;%dc-colon;description">
<!ENTITY % dc-date        "%dc-prefix;%dc-colon;date">

Warning

Do not omit this step and try to use the dc-prefix and dc-colon parameter entities directly in ELEMENT and ATTLIST declarations. This will fail because XML parsers add extra space around the entity’s replacement text when they’re used outside another entity’s replacement text.

Then you use the entity references for the qualified name in all declarations, like this:

<!ELEMENT %dc-title; (#PCDATA)> <!ELEMENT %dc-creator; (#PCDATA)> <!ELEMENT %dc-description; (#PCDATA)> <!ELEMENT %dc-date; (#PCDATA)> <!ELEMENT rdf:Description ((%dc-title; | %dc-creator; ...