code: public static <PS, SEG, S> UndoManager<List<PlainTextChange>> plainTextUndoManager(
              GenericStyledArea<PS, SEG, S> area) {
          return plainTextUndoManager(area, DEFAULT_PREVENT_MERGE_DELAY);
      }
docs: Returns an UndoManager with an unlimited history that can undo/redo {@link PlainTextChange}s. New changes
  emitted from the stream will not be merged with the previous change
  after {@link #DEFAULT_PREVENT_MERGE_DELAY}