This is the version of halfspace that was used in the calculations for "The weight of the mountains: Constraints on tectonic stress, friction, and fluid pressure in the 2008 Wenchuan earthquake from estimates of topographic loading" by R. Styron and E. Hetland, 2015, Journal of Geophysical Research: Solid Earth.
Future versions will have some refactoring (notably a change from a left-handed coordinate system, in E, N, D coords, to a right-handed coordinate system, t.b.d). This will almost certainly break something in the JGR calculations. So if you want to reproduce any of that business, use this version.