Planning a 4x2 construction with DF's `umkh` keys (i.e. not automaterial's box-select) would previously produce a 5x3 construction instead, for example.
DFHack is a Dwarf Fortress memory access library, distributed with scripts
and plugins implementing a wide variety of useful functions and tools.
The full documentation is available online here,
from the README.html page in the DFHack distribution, or as raw text in the ./docs folder.
If you're an end-user, modder, or interested in contributing to DFHack -
go read those docs.
If that's unclear or you need more help, try
the Bay12 forums thread
or the #dfhack IRC channel on freenode.