RELAX NG

Which Library Should Be Used?

All the RELAX NG implementations must support the native datatype library; many of them also support the DTD compatibility datatypes library and the W3C XML Schema datatypes library. That means that if you want to define a token or string datatype, you can often choose between the native library and W3C XML Schema datatypes, and if you’re defining ID, IDREF, or IDREFS, you can often choose between the DTD compatibility library and W3C XML Schema datatypes.

Native Types Versus W3C XML Schema Datatypes

The criteria for choosing between native or W3C XML Schema datatypes to define string and token types is simple: if you need facets, use W3C XML Schema datatypes. If you don’t, use native datatypes: your schema will be more portable, because the RELAX NG processors aren’t obliged to support the W3C XML Schema type library.

DTD Versus W3C XML Schema Datatypes

When you need to define a datatype covered by both DTD and W3C XML Schema—i.e., ID, IDREF, or IDREFS—a similar rule of thumb applies. If you use the DTD compatibility library, your schema should be slightly more portable, but you will lose the facets.

The other factor to take into account is that the rules applied when you use the DTD compatibility feature are strict and consistent over different implementations; when you use the W3C XML Schema type library, a processor should apply these same rules if and only if it also supports the DTD datatype library. Processors that support only W3C XML Schema datatypes ...