|Attribute represents an XML-style attribute of an
Element. Typically, the allowable values are controlled by its
declaration in the Document Type Definition (DTD) governing this
kind of document.
If the attribute has not been explicitly assigned a value, but has
been declared in the DTD, it will exist and have that default. Only
if neither the document nor the DTD specifies a value will the
Attribute really be considered absent and have no value; in that
case, querying the attribute will return null.
Attributes may have multiple children that contain their data. (XML
allows attributes to contain entity references, and tokenized
attribute types such as NMTOKENS may have a child for each token.)
For convenience, the Attribute object's getValue() method returns
the string version of the attribute's value.
Attributes are not children of the Elements they belong to, in the
usual sense, and have no valid Parent reference. However, the spec
says they _do_ belong to a specific Element, and an INUSE exception
is to be thrown if the user attempts to explicitly share them
Note that Elements do not permit attributes to appear to be shared
(see the INUSE exception), so this object's mutability is
officially not an issue.
DeferredAttrImpl inherits from AttrImpl which does not support
Namespaces. DeferredAttrNSImpl, which inherits from AttrNSImpl, does.