anchor.diff:  %% isn't a list.<br/>
   %% Raises `{invalid_label_name, Name, Message}' error if `Name' isn't a valid
   %% label name.<br/>
  -%% Raises `{invalid_value_error, Value, MessagE}' error if `duration_unit' is
  -%% unknown or doesn't match metric name.<br/>
   %% @end
   declare(Spec) ->
     prometheus_metric:insert_mf(?TABLE, ?MODULE, Spec).
  
positive.code: %% isn't a list.<br/>
  %% Raises `{invalid_label_name, Name, Message}' error if `Name' isn't a valid
  %% label name.<br/>
  %% Raises `{invalid_value_error, Value, Message}' error if `duration_unit' is
  %% unknown or doesn't match metric name.<br/>
  %% Raises `{mf_already_exists, {Registry, Name}, Message}' error if a boolean
  %% with the same `Spec' already exists.
  %% @end
  
negative.code: %% @doc Returns the value of the boolean identified by `Registry', `Name'
  %% and `LabelValues'. If there is no boolean for `LabelValues',
  %% returns `undefined'.
  %%
  %% Raises `{unknown_metric, Registry, Name}' error if boolean named `Name'
  %% can't be found in `Registry'.<br/>
  