The public identifier associated with the entity if specified, and
NULL otherwise.
systemId
The system identifier associated with the entity if specified, and
NULL otherwise. This may be an absolute URI or not.
notationName
For unparsed entities, the name of the notation for the entity. For
parsed entities, this is NULL.
actualEncoding
An attribute specifying the encoding used for this entity at the
time of parsing, when it is an external parsed entity. This is
NULL if it an entity from the internal subset or if it is not
known.
encoding
An attribute specifying, as part of the text declaration, the
encoding of this entity, when it is an external parsed entity. This
is NULL otherwise.
version
An attribute specifying, as part of the text declaration, the
version number of this entity, when it is an external parsed
entity. This is NULL otherwise.