The dash definitions are simple and look remarkably like the definitions for noncontinuous linetypes in September 1999's Learning Curve. All you need to do is specify a length for each segment. Lengths of 0 and 20 both produce a dot. AutoCAD allows you to append up to six dash specifications to the line specification. This causes each succeeding line to shift toward the left.
Negative values produce a shift in the opposite direction.
This is a good time to bring up another significant point. Hatch patterns consist of line segments, so they take on the linetype of the current layer. You should almost always specify a continuous linetype for the layer on which hatching occurs, because any noncontinuous linetype interacts with any dashed lines specified within the hatch pattern, leading to bizarre results. When I started to play with complex hatch pattern definitions, I expected to find something that worked like an array, where all I had to do was define one copy of the pattern, then specify a repetition spacing for multiple copies. Unfortunately, complex hatching in AutoCAD works on a completely different principle.