bread crumbs

bread crumbs
 n.

   1. Debugging statements inserted into a program that emit output or
   log indicators of the program's {state} to a file so you can see where
   it dies or pin down the cause of surprising behavior. The term is
   probably a reference to the Hansel and Gretel story from the Brothers
   Grimm or the older French folktale of Thumbelina; in several variants
   of these, a character leaves a trail of bread crumbs so as not to get
   lost in the woods.

   2. In user-interface design, any feature that allows some tracking of
   where you've been, like coloring visited links purple rather than blue
   in Netscape (also called footprinting).