docs: def migrate_process_schema(self, process, schema, from_state):
          """Migrate process schema.
  
          :param process: Process instance
          :param schema: Process schema to migrate
          :param from_state: Database model state
          :return: True if the process was migrated, False otherwise
          """
          container = dict_dot(schema, '.'.join(self.field[:-1]), default=list)
  
          # Ignore processes, which already contain the target field with the
          # target schema.
          for field in container:
              if field['name'] == self.field[-1]:
                  if field == self.schema:
                      return False
                  else:
                      raise ValueError(
                          "Failed to migrate schema for process '{process}' as the field '{field}' "
                          "already exists and has an incompatible schema".format(
                              process=process.slug,
                              field=self.field[-1]
                          )
                      )
  
          # Add field to container.
          container.append(self.schema)
          return True