docs: def _construct_qs_filter(self, field_name):
          """
          Using a field name optionnaly prefixed by `^`, `=`, `@`, return a
          case-insensitive filter condition name usable as a queryset `filter()`
          keyword argument.
          """
          if field_name.startswith('^'):
              return "%s__istartswith" % field_name[1:]
          elif field_name.startswith('='):
              return "%s__iexact" % field_name[1:]
          elif field_name.startswith('@'):
              return "%s__search" % field_name[1:]
          else:
              return "%s__icontains" % field_name