 The development branch then began the largest period of code work since before Leffler released 4.0pl0.The Class 1 driver was endowed with ECM capability, fax batching support (sending multiple faxes in one call) was added, extended resolution support began, MMR and JBIG data compressions were supported, and color fax reception was supported all in a relatively short amount of time.This set of developments, and the subsequent stabilization of those features, made HylaFAX not only the best, most feature-rich open-source fax software available, but it also became easily the most feature-rich fax software of any kind that supported average, inexpensive off-the-shelf fax modems.