The root element identifying a RelaxNG grammar.
<grammar xmlns="http://relaxng.org/ns/structure/1.0"> <start> ... </start> <define name="def1"> ... </define> <define name="def2"> ... </define> </grammar>
A grammar element has one 'start' child-element.
A grammar element can have multiple 'define' child-elements.
RelaxNG Namespace: http://relaxng.org/ns/structure/1.0