The output RELAX NG schema is designed to constrain only the value of selector, nothing else. Thus it allows any outermost (“root”) element from any namespace (including the null namespace), which is allowed to have any attributes from any namespace (including the null namespace) and any children including text intermingled with any number of any element from any namespace (including the null namespace); each child element in turn is also allowed to have any attributes from any namespace (including the null namespace) and any children including text intermingled with any number of any element from any namespace (including the null namespace), except that any selector attribute on any element must match the generated regular expression. Thus the only error messages generated by validation against the schema assert that the value of a selector attribute is not a CSS3 selector.^[40]

The main declaration of the RELAX NG schema is shown in Figure 1, “RELAX NG schema constraint”; the placeholder GENERATED_REGEXP_HERE indicates where in the schema the generated regular expression is placed. The schema is shown in the compact syntax although it is generated in the XML syntax.

start = ANY
ANY =
  element * {
    attribute * - selector { text }*,
    attribute selector {
      xsd:string {
        pattern = "GENERATED_REGEXP_HERE"
      }
    }?,
    (text | ANY)*
  }