DOC: Make the comment slightly clearer

Author: MechCoder

sklearn/preprocessing/data.py

@@ -1061,9 +1061,10 @@ def _transform(self, X):
                              " Expected %d, got %d."
                              % (indices.shape[0] - 1, n_features))
 
-        # We mask those features of X are unknown, i.e less than n_values_
-        # If self.handle_unknown is "ignore", the row_indices and col_indices
-        # corresponding to the unknown categorical feature are masked.
+        # We use only those catgorical features of X that are known using fit.
+        # i.e lesser than n_values_ using mask.
+        # This means, if self.handle_unknown is "ignore", the row_indices and
+        # col_indices corresponding to the unknown categorical feature are ignored.
         mask = (X < self.n_values_).ravel()
         if np.any(~mask):
             if self.handle_unknown not in ['error', 'ignore']: