There are several rules that apply to binding declarations made in an external binding customization file that do not apply to similar declarations made inline in a source schema:
The binding customization file must begin with the jxb:bindings version attribute, plus attributes for the JAXB and XMLSchema namespaces:
<jxb:bindings version="1.0" xmlns:jxb="http://java.sun.com/xml/ns/jaxb" xmlns:xs="http://www.w3.org/2001/XMLSchema">
The remote schema to which the binding declaration applies must be identified explicitly in XPath notation by means of a jxb:bindings declaration specifying schemaLocation and node attributes:
schemaLocation specifies a URI reference to the remote schema.
node specifies an XPath 1.0 expression that identifies the schema node within schemaLocation to which the given binding declaration is associated; in the case of the initial jxb:bindings declaration in the binding customization file, this node is typically "/xs:schema".
Similarly, individual nodes within the schema to which customizations are to be applied must be specified using XPath notation; for example:
In such cases, the customization is applied to the node by the binding compiler as if the declaration was embedded inline in the node’s <xs:appinfo> element.
To summarize these rules, the external binding element <jxb:bindings> is only recognized for processing by a JAXB binding compiler in three cases:
When its parent is an <xs:appinfo> element.
When it is an ancestor of another <jxb:bindings> element.
When it is the root element of a document. An XML document that has a <jxb:bindings> element as its root is referred to as an external binding declaration file.