1.3. X-script of elements and text nodes

Let's now show how to specify child nodes of an element and how to write the X-script of elements. The X-script of an element must be written in the special attribute “xd:script” (the prefix "xd" must correspond to the namespace of X-definition: "http://www.xdef.org/xdef/4.2").
In the example below we added the child elements "Title" and "Author". Both child elements contain a required text node. The X-script of the text node is written as a value of text node. We consider there are books with one author, more authors, or even without an author. Therefore the quantifier of the element "Author" is specified as "occurs *" (i.e. none or more occurrences) in the X-script of the element model. However, the child element "Title" must be one (i.e. it is required):

<Book isbn="required int(10000000, 999999999);"
      published="optional gYear();" > 
  <Author xd:script="occurs *;" >
        required string(); /* name of author */"
  <Title xd:script="required;" >
        required string(); /* title of the book */"

Since the default value of quantifier is "required" notice that the specification of such quantifier can be omitted:

<Book isbn="int(0, 9999999999);" published="optional gYear();" >
  <Author xd:script="occurs *;" > string(); </Author>
  <Title string(); </Title>