After a weak two bid and a takeout double, the opener's partner may bid

The lead directors are useful since the weak two bidder will frequently be on lead after a takeout double in direct seat. Some people play a variation of this gadget in which redouble is natural, new suits at the 2 level are to play, and 2N forces 3c to sign off at the 3 level somewhere. If you choose to play that variation, you can redouble and bid a new suit to show a forcing one suiter. Either of these variations is infinitely superior to standard.

source: (Kent Feiler)