docs: function () {
  
      /*  Tagging arbitrary member as $final
          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
  
          $assertThrows (function () {
  
              var A = $prototype ({
                          constructor: $final (function () {}) })
  
              var B = $extends (A, {
                          constructor: function () {} }) },   // will throw Error
  
              _.matches ({ message: 'Cannot override $final constructor' }))
  
      /*  Tagging whole prototype as $final
          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
  
          $assertThrows (function () {
  
              var A = $prototype ($final ({}))
              var B = $extends (A) }, // will throw Error
  
               _.matches ({ message: 'Cannot derive from $final-marked prototype' })) }