RELAX NG

Whitespace and RELAX NG Native Datatypes

RELAX NG includes a native type system, but this type library has been kept minimal by design because more complete type libraries are available. It consists of just two datatypes (token and string) that differ only in the whitespace processing applied before validation. The whole RELAX NG datatype system can be seen as a mechanism for adding validating transformations to text nodes. These transformations change text nodes into canonical formats (formats in which all the different formats for a same value are converted into a single normalized or “canonical” format). The two native datatypes don’t detect format errors (their formats are broad enough to allow any value) but still transform text nodes in their canonical forms, which can make a difference for enumerations. Other datatype libraries, covered in Chapter 8, can detect format errors.

Enumerations are the first place you can see datatypes at work. Applying datatypes to enumeration values is done by adding a type attribute in value patterns. Up to now, we haven’t specified any datatype when we’ve written value elements. By default, they have the default type token from the built-in library. Text values of this datatype receive full whitespace normalization similar to that performed by the XPath normalize-space( ) function: all sequences of one or more whitespace characters—the characters #x20 (space), #x9 (tab), #xA (linefeed), and #xD (carriage return)—are replaced by a single ...