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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def build_doctype(qualifiedName, publicId=None, systemId=None, internalSubset=None):
 """ Instantiate an ElifeDocumentType, a subclass of minidom.DocumentType, with some properties so it is more testable """

    doctype = ElifeDocumentType(qualifiedName)
    doctype._identified_mixin_init(publicId, systemId)
    if internalSubset:
        doctype.internalSubset = internalSubset
    return doctype