docs: def modname_source_to_target(
              self, toolchain, spec, modname, source):
          """
          This is called by the Toolchain for modnames that contain a '!'
          as that signifies a loaderplugin syntax.  This will be used by
          the toolchain (which will also be supplied as the first argument)
          to resolve the copy target, which must be a path relative to the
          spec[WORKING_DIR].
  
          If the provided modname points contains a chain of loaders, the
          registry associated with this handler instance will be used to
          resolve the subsequent handlers until none are found, which that
          handler will be used to return this result.
          """
  
          stripped_modname = self.unwrap(modname)
          chained = (
              self.registry.get_record(stripped_modname)
              if '!' in stripped_modname else None)
          if chained:
              # ensure the stripped_modname is provided as by default the
              # handler will only deal with its own kind
              return chained.modname_source_to_target(
                  toolchain, spec, stripped_modname, source)
          return stripped_modname