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5. The definition patterns

To write an RNC schema, use start construct to define what content can go into the root element. The remainder of the schema can be placed inside the start construct, or you can break the schema up into named parts and use references to those names to connect the parts of the schema to the start construct.

namespace ns ="URI"

Define a namespace prefix ns using the given URI. For example:

    namespace xsl = "http://www.w3.org/1999/XSL/Transform"

After the above definition, a tag name such as xsl:comment would match only tags in the namespace given by that URI.

default namespace = "URI"

Define the default namespace.

grammar { definition ... }

The top level of schema definitions. Should include a start definition.

start = definition

Declares the content of the root element of the document type.

name = definition

Names a pattern. You can use such names anywhere a pattern or definition is allowed.

element name { p }

Specifies that in this document type, the content of element name must match p.

An element construct is just another pattern, which you can nest. For example:

    element name {
      element first { text },
      element last { text }
    }

This specifies that a name element must contain a first element followed by a last element.

You can also use the postfix operators *, +, and ? after the closing brace, for example:

    element q-and-a {
      element question { text },
      element answer { text }*
    }

This rule defines the content of a q-and-a element as one question element followed by zero or more answer elements.

attribute aname { p }

Used inside an element construct to specify that the element must have an attribute named aname.

list { p }

Matches a whitespace-separated list of patterns that match p.

For example, this pattern would require that a scores element contain a space-separated list scores="i0 f0 i1 f1 …", where each ik is an integer, and each fk is a float (type xsd:double):

    attribute scores {
      list { (xsd:int, xsd:double)+ }
    }
mixed { p }

Matches any mixture of text and pattern p.

empty

Used to declare that an element has no content. For example:

    element newPage { empty }
external "filename"

Matches the RNC patterns defined in file filename.

include "filename"

Merges with the current grammar the grammar from the named file.

include "filename" { defs }

Merge the named file into the current grammar, but replace any definitions from that file with defs, the definitions between the braces.

# comment

#” is the comment character in RNC. Any characters on a line following # will be ignored.

## annotation

Lines starting with ## are special comments that are treated as annotations to the material that follows. Some tools may allow you to retrieve the annotations for a given pattern.