old_contents: import sublime
  import sublime_plugin
  
  
  class MoveByLinesCommand(sublime_plugin.TextCommand):
  
      def run(self, edit, forward=True, number_of_lines=1):
          for _ in range(number_of_lines):
              self.view.run_command('move', {"by": "lines", "forward": forward})
  
new_contents: import sublime
  import sublime_plugin
  
  
  class MoveByLinesCommand(sublime_plugin.TextCommand):
  
      def run(self, edit, forward=True, extend=False, number_of_lines=1):
          for _ in range(number_of_lines):
              self.view.run_command('move', {"by": "lines", "forward": forward, "extend": extend})
  
subject: Support for extend