code: def setup(app):
      ''' Required Sphinx extension setup function. '''
      app.add_node(
          collapsible_code_block,
          html=(
              html_visit_collapsible_code_block,
              html_depart_collapsible_code_block
          )
      )
      app.add_directive('collapsible-code-block', CollapsibleCodeBlockf setup(app):
      ''' Required Sphinx extension setup function. '''
      app.add_node(
          collapsible_code_block,
          html=(
              html_visit_collapsible_code_block,
              html_depart_collapsible_code_block
          )
      )
      app.add_directive('collapsible-code-block', CollapsibleCodeBlock)
docs: Required Sphinx extension setup function.