What does the suffix "-wise" mean in general, for example in "clockwise" or "lengthwise"? Clockwise: in the direction of a clock, the way of a clock. Lengthwise: in the direction of the length, the way of the length (of something). Otherwise: in an other way, a way other (than expected).
I guess "-wise" (ways) is related to "-wards", though "-wards" is more directional (in terms of spatial relations) than "-ways" (which is more the manner, or way, in which something is done). Towards, inwards, outwards; and you wouldn't really say "stringwards", I don't think.
Anyways.... that's a Perlmonkwise explanation of "stringwise". ^.^