Starts a new non-text element as a child of the current element.
Each such call should be ended with corresponding end_element. Use
null ns_href, to use the default namespace, otherwise either previously added namespace
with the same href from e_xml_document_add_namespaces is picked, or a new namespace with generated prefix is added.
To start a text node use start_text_element.
| this |
an XmlDocument |
| ns_href |
optional namespace href for the new element, or null |
| name |
name of the new element |