RELAX NG

Data Versus Text

In Chapter 6, I provided a detailed description of the text pattern and its behavior within interleave patterns. There’s another pattern that also describes and attaches datatypes to text nodes. Even though this pattern will become more useful with the introduction of the datatype libraries in Chapter 8, it’s worth examining its core features right now to be sure you’ve touched on most of the definitions related to nodes.

The data pattern accepts a type attribute (as for the value pattern) and checks that the value is valid per this type. Since our two built-in types accept any value, the data pattern with built-in types is almost equivalent to a text pattern. However, the data pattern doesn’t mean, like the text pattern, “zero or more text nodes” but instead “one text node.” The data pattern has been designed to represent data. It’s forbidden in mixed-content models because the authors of the RELAX NG specification considered mixing data and elements poor practice.

This restriction applies to all patterns that match a single text node (data, value, and list) that can never be associated with patterns matching sibling elements (elements that can add the same parent element in the same instance document). In practice, this means you can’t use a data pattern to describe content models such as:

 <price><currency>USD</currency>20</price>

or:

 <price>20<currency>Euro</currency></price>

These content models were considered poor practice by the authors of the RELAX NG specification. ...