The New wizard only creates a skeleton document containing the document prolog, a root element and possibly other child elements depending on the options specific for each schema type. If you need to generate full and valid XML instance documents based on an XML Schema schema, you should use the XML instance generation tool instead.
The Oxygen plugin installs a series of Eclipse wizards for easy creation of new documents. Using these wizards you let Oxygen complete details like the system ID or schema location of a new XML document, the minimal markup of a DocBook article or the namespace declarations of a Relax NG schema.
For example if XML was selected the Create an XML Document wizard is started.
The Create an XML Document dialog enables definition of an XML Document Prolog using the system identifier of an XML Schema, DTD, Relax NG (full or compact syntax) schema, or NVDL (Namespace-based Validation Dispatching Language) schema. As not all XML documents are required to have a Prolog, you may choose to skip this step by clicking OK. If the prolog is required, complete the fields as described in the next step.