purpose of "vpath" for Config.in in Makefile?

[Robert P. J. Day]

what is the purpose of the line:

  vpath %/Config.in $(srctree)

in the top-level Makefile?  AFAIK, the vpath directive affects only
the search path for *dependencies* but, from what i read, all of the
Config.in files in the source tree are never treated as dependencies.

rather, they're "source"d from that top-level Config.in file which
doesn't seem to have anything to do with vpath.  or are they being
used as dependencies somewhere that i just didn't notice?

rday