code: def get_insertion(cls) -> str:
          
          indent = 1
          blanks = ' ' * (indent+4)
          subs = []
          for name in cls.get_modelnames():
              subs.extend([
                  f'{blanks}<element name="{name}"',
                  f'{blanks}         substitutionGroup="hpcb:sequenceGroup"',
                  f'{blanks}         type="hpcb:{name}Type"/>',
                  f'',
                  f'{blanks}<complexType name="{name}Type">',
                  f'{blanks}    <complexContent>',
                  f'{blanks}        <extension base="hpcb:sequenceGroupType">',
                  f'{blanks}            <sequence>'])
              model = importtools.prepare_model(name)
              subs.append(cls.get_modelinsertion(model, indent + 4))
              subs.extend([
                  f'{blanks}            </sequence>',
                  f'{blanks}        </extension>',
                  f'{blanks}    </complexContent>',
                  f'{blanks}</complexType>',
                  f''
              ])
          return '\n'.join(subs)
docs: Return the complete string to be inserted into the string of the
          template file.
  
          >>> from hydpy.auxs.xmltools import XSDWriter
          >>> print(XSDWriter.get_insertion())    # doctest: +ELLIPSIS
               <element name="arma_v1"
                        substitutionGroup="hpcb:sequenceGroup"
                        type="hpcb:arma_v1Type"/>
          <BLANKLINE>
               <complexType name="arma_v1Type">
                   <complexContent>
                       <extension base="hpcb:sequenceGroupType">
                           <sequence>
                              <element name="fluxes"
                                       minOccurs="0">
                                  <complexType>
                                      <sequence>
                                          <element
                                              name="qin"
                                              minOccurs="0"/>
          ...
                                  </complexType>
                              </element>
                           </sequence>
                       </extension>
                   </complexContent>
               </complexType>
          <BLANKLINE>