code: def manual():
      """
      Returns the general manual of Optunity, with a brief introduction of all registered solvers.
  
      :returns: the manual as a list of strings (lines)
      """
      global __registered_solvers
      manual = [
          "Optunity: optimization algorithms for hyperparameter tuning",
          " ",
          "The following solvers are available:",
      ]
      for name, cls in __registered_solvers.items():
          manual.append(name + " :: " + cls.desc_brief)
      manual.append(" ")
      manual.append(
          "For a solver-specific manual, include its name in the request."
      )
      manual.append(
          "For more detailed info, please consult the Optunity documentation at:"
      )
      manual.append("http://docs.optunity.net")
      return manual
  
label_desc: Use image node_id 3 for calling a global function with example usage: manual() and returns: manual