.for .. .endfor (in kcgi - Makefile)

i tried to find documentation, but no success

Makefile:157: *** missing separator.  Stop.

s1 = x \
        y \
        z

s2 = a

d =
.for e in ${s1} ${s2}
  d += ${e}.htm
.endfor

make -v -> 4.3 , update -> 4.4.1 (both version)

i tried in extra makefile, simple as possible, but did not help
ld =
ls = a b c
.for e in ${ls}
  ld += ${e}
.endfor

thanks in advance, Andreas