code: def build_extension_item(name: str, parameters: List[ExtensionParameter]) -> str:
      
      return "; ".join(
          [name]
          + [
              # Quoted strings aren't necessary because values are always tokens.
              name if value is None else f"{name}={value}"
              for name, value in parameters
          ]
      )
docs: Build an extension definition.
  
      This is the reverse of :func:`parse_extension_item`.