Namespace URI to use to represent that there is no Namespace.

Defined by the Namespace specification to be "".

Also see:

Namespaces in XML, 5.2 Namespace Defaulting

Prefix to use to represent the default XML Namespace.

Defined by the XML specification to be "".

Also see:

Namespaces in XML, 3. Qualified Names

The official XML Namespace name URI.

Defined by the XML specification to be "http://www.w3.org/XML/1998/namespace".

Also see:

Namespaces in XML, 3. Qualified Names

The official XML Namespace prefix.

Defined by the XML specification to be "xml".

Also see:

Namespaces in XML, 3. Qualified Names<

The official XML attribute used for specifying XML Namespace declarations, XMLConstants.XMLNS_ATTRIBUTE , Namespace name URI.

Defined by the XML specification to be "http://www.w3.org/2000/xmlns/".

Also see:

Namespaces in XML, 3. Qualified Names
Namespaces in XML Errata

The official XML attribute used for specifying XML Namespace declarations.

It is NOT valid to use as a prefix. Defined by the XML specification to be "xmlns".

Also see:

Namespaces in XML, 3. Qualified Names

W3C XML Schema Namespace URI.

Defined to be "http://www.w3.org/2001/XMLSchema".

Also see:

XML Schema Part 1: Structures, 2.6 Schema-Related Markup in Documents Being Validated

W3C XML Schema Instance Namespace URI.

Defined to be "http://www.w3.org/2001/XMLSchema-instance".

Also see:

XML Schema Part 1: Structures, 2.6 Schema-Related Markup in Documents Being Validated

W3C XPath Datatype Namespace URI.

Defined to be "http://www.w3.org/2003/11/xpath-datatypes".

Also see:

XQuery 1.0 and XPath 2.0 Data Model

XML Document Type Declaration Namespace URI as an arbitrary value.

Since not formally defined by any existing standard, arbitrarily define to be "http://www.w3.org/TR/REC-xml". 

RELAX NG Namespace URI.

Defined to be "http://relaxng.org/ns/structure/1.0".

Also see:

RELAX NG Specification

Feature for secure processing.

• true instructs the implementation to process XML securely. This may set limits on XML constructs to avoid conditions such as denial of service attacks.
• false instructs the implementation to process XML acording the letter of the XML specifications ingoring security issues such as limits on XML constructs to avoid conditions such as denial of service attacks.