title: Unable to append the gml string to xml using lxml in python
body: <p>test_gml.py</p>
  
  <pre><code>from lxml import etree
  import lxml
  xml_response = lxml.etree.Element('xmlResponse')
  mapping = lxml.etree.SubElement(xml_response,'mapping',{"id":"AHGJHKSHQWEIUELQWDKJQEDH"})
  services_element = lxml.etree.SubElement(mapping, 'service_name')
  services_element.text = "gml_info"
  gml_info = '''&lt;gml:Envelope srsName="EPSG:4326"&gt;
          &lt;gml:lowerCorner&gt;1 2&lt;/gml:lowerCorner&gt;
          &lt;gml:upperCorner&gt;10 20&lt;/gml:upperCorner&gt;
      &lt;/gml:Envelope&gt;'''
  services_element = lxml.etree.SubElement(mapping, 'gml_info')
  services_element.text = gml_info
  print (etree.tostring(xml_response))
  </code></pre>
  
  <p>When I try to run the above code I am getting the below response where gml tags are not preserved.</p>
  
  <p>Response:</p>
  
  <pre><code>b'&lt;xmlResponse&gt;&lt;mapping id="AHGJHKSHQWEIUELQWDKJQEDH"&gt;
  &lt;service_name&gt;gml_info&lt;/service_name&gt;
  &lt;gml_info&gt;&amp;lt;gml:Envelope 
  srsName="EPSG:4326"&amp;gt;\n\t\t&amp;lt;gml:lowerCorner&amp;gt;1 
  2&amp;lt;/gml:lowerCorner&amp;gt;\n\t\t&amp;lt;gml:upperCorner&amp;gt;10 
  20&amp;lt;/gml:upperCorner&amp;gt;\n\t&amp;lt;/gml:Envelope&amp;gt;&lt;/gml_info&gt;
  &lt;/mapping&gt;&lt;/xmlResponse&gt;'
  </code></pre>