This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.
This property exists on all nodes (HTML, XUL, SVG, MathML, etc.), but only if the script trying to use it has UniversalXPConnect privileges.
Node.baseURI for details on what the base URL is.
uriObj = node.baseURIObject
This property is read-only; attempting to write to it will throw an exception. In addition, this property may only be accessed from privileged code.
Not in any specification.