The feature I am requesting is to be able to get the systemId() from
DocumentType interface. Currently DocumentType interface doesn't have any
API to access the system id for the DTD. Although, in the implementation
class of DocumentType, i.e. DocType, it maintains the system id and public
id. These ids are used to print in the DOCTYPE declaration when you generate
XML back from the XmlDocument. I have checked from DOM Level 2
Specification, It is defined in DOM Level 2 spec.

Please suggest if it is feasible for you to accommodate this feature-request
as part of current release.