default-content-type
If present, this element indicates that its parent
content-type
element represents the default
content type of this publication and may be treated accordingly in
client applications. This element only has meaning as the child of a
content-type
element, and it should not
appear more than once in a content-type
resource. The result of specifying the element more than once is
undefined.
Syntax
<default-content-type/>