A proper file looks like a CSV (comma-separated) with grid points marked for 'd'igging (or other designate options such as ramps and stairs).
It starts with a #dig header such as:
#dig start(1,1)
or
#dig start(64,64) Giant swirly spiral starting at center of 128-wide square
#dig start(1,1) ,d, d, ,d ,d,d