code: def get_exchangeinsertion(cls):
          
          indent = 1
          subs = [cls.get_mathitemsinsertion(indent)]
          for groupname in ('setitems', 'additems', 'getitems'):
              subs.append(cls.get_itemsinsertion(groupname, indent))
              subs.append(cls.get_itemtypesinsertion(groupname, indent))
          return '\n'.join(subs)
docs: Return the complete string related to the definition of exchange
          items to be inserted into the string of the template file.
  
          >>> from hydpy.auxs.xmltools import XSDWriter
          >>> print(XSDWriter.get_exchangeinsertion())    # doctest: +ELLIPSIS
              <complexType name="arma_v1_mathitemType">
          ...
              <element name="setitems">
          ...
              <complexType name="arma_v1_setitemsType">
          ...
              <element name="additems">
          ...
              <element name="getitems">
          ...