DocumentType | NN 6 IE 5(Mac) DOM 1
Reflects the DOCTYPE element, if one arrives to the browser as part of the document flow. The DocumentType object is its own node type in the W3C DOM, and, just as indicated in its position in a document's source code, exists outside of the content portion of the document tree. Access to this object in supported browsers is via the document.doctype property. If no DOCTYPE element exists in the file, the property returns null.
Properties of the DocumentType object expose individual pieces of the data within the DOCTYPE tag, whose structure is determined by SGML standards. The W3C DOM Level 2 specification provides placeholder properties for these pieces, and Netscape 6 implements most of them to one degree or other. But it is clear from the DOM specification that work on aligning the two worlds is not complete.
Object Model Reference
    documentTypeNodeReference
Object-Specific Properties

entities | internalSubset | name | notations | publicId | systemId

Object-Specific Methods
None.
Object-Specific Event Handler Properties
None.

entities | NN 6 IE n/a DOM 1
| Read-only
Returns an array of nested Entity nodes within the DOCTYPE element. An Entity is formatted according to the following syntax (which would appear inside the DOCTYPE element's angle brackets):
    <!ENTITY [publicID "systemID>]"
Primarily applicable to XML documents.
Value
Array (technically, a NamedNodeMap data type) of Entity node object references.
Default
null

internalSubset | NN 6 IE n/a DOM 2
| Read-only
Returns a string value of the internal subset portion of the element.
Value
String.
Default
Empty string.

name | NN 6 IE 5(Mac) DOM 1
| Read-only
Returns a string value of the name portion of the element. The name is the first word that follows the DOCTYPE element's tag name. In the context of this book's subject, all HTML and XHTML documents show this value to be html. Note that although this object and property are implemented in IE 5/Macintosh, that browser returns the entire inner string value of the DOCTYPE element, starting with the html name.
Value
String.
Default
html

notations | NN 6 IE n/a DOM 1
| Read-only
Returns an array of references to Notation nodes within the DOCTYPE element.
Value
Array (technically, a NamedNodeMap data type) of Notation node object references.
Default
null

publicId | NN 6 IE n/a DOM 2
| Read-only
Returns a string value of the public identifier portion of the element. This data reveals the type of DTD, as in "-//W3C//DTD XHTML 1.0 Strict//EN".
Value
String.
Default
Empty string.

systemId | NN 6 IE n/a DOM 2
| Read-only
Returns a string value of the system identifier portion of the element. This data typically reveals the URI of DTD, as in "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd".
Value
String.
Default
Empty string.