module DocumentNumbering

def auto_doc_number!

document numbering is desired.
construction, which should be blank if auto
Convenience method for proper AutoDocNumber tag 
def auto_doc_number!
  self.auto_doc_number = ''
end

def document_numbering 

def document_numbering
  if !auto_doc_number.nil? && !doc_number.nil?
    errors.add(:doc_number, "DocumentNumber should not be specified if AutoDocNumber is.")
  end
end