docs: def clear(**kwargs):
      """Clear the specified names from the specified databases.
  
      This can be highly destructive as it destroys tables and when all names
      are removed from a database, the database itself.
      """
  
      database = kwargs.pop('database', False)
      expression = lambda target, table: table.drop(target)
      test = lambda x, tab: not database_exists(x.url) or not tab.exists(x)
  
      # TODO: Iterate through all engines in name set.
      if database and database_exists(engine['default'].url):
          drop_database(engine['default'].url)
          clear_cache()
  
      op(expression, reversed(metadata.sorted_tables), test=test,
         primary='clear', secondary='drop', **kwargs)