Originally Posted by Wilfred Laurier

I don't have a photo.

But the tab would be part of a washer under the cable fixing bolt on the front derailleur, directly behind and obscured by the fixing bolt in the front derailleur pic you posted. The cable must run over the tab instead of under it. Routing it over the tab makes the lever arm of the derailleur slightly longer so it requires less tension to move the derailleur, but moves slightly less with each mm of cable movement.
If the cable is routed under this tab, the derailleur will be much more difficult to move, and the indexing (if it is indexed) will not work properly.