code: def merge_xml(first_doc, second_doc):
      
      # Adapted from:
      # http://stackoverflow.com/questions/27258013/merge-two-xml-files-python
      # Maps each elements tag to the element from the first document
      if isinstance(first_doc, lxml.etree._Element):
          first_doc = ET.fromstring(lxml.etree.tostring(first_doc))
      if isinstance(second_doc, lxml.etree._Element):
          second_doc = ET.fromstring(lxml.etree.tostring(second_doc))
      mapping = {element.tag: element for element in first_doc}
      for element in second_doc:
          if not len(element):
              # Recursed fully.  This element has no children.
              try:
                  # Update the first document's element's text
                  mapping[element.tag].text = element.text
              except KeyError:
                  # The element doesn't exist
                  # add it to the mapping and the root document
                  mapping[element.tag] = element
                  first_doc.append(element)
          else:
              # This element has children.  Recurse.
              try:
                  merge_xml(mapping[element.tag], element)
              except KeyError:
                  # The element doesn't exist
                  # add it to the mapping and the root document
                  mapping[element.tag] = element
                  first_doc.append(element)
      return lxml.etree.fromstring(ET.tostring(first_doc))
docs: Merges two XML documents.
  
      Args:
          first_doc (str): First XML document.  `second_doc` is merged into this
              document.
          second_doc (str): Second XML document.  It is merged into the first.
  
      Returns:
          XML Document: The merged document.
  
      Raises:
          None
  
      Example:
          >>> import pynos.utilities
          >>> import lxml
          >>> import xml
          >>> x = xml.etree.ElementTree.fromstring('<config />')
          >>> y = lxml.etree.fromstring('<config><hello /></config>')
          >>> x = pynos.utilities.merge_xml(x, y)