This document describes how to convert freeciv 3.0 compatible ruleset to development version (one that will become freeciv 3.1) compatible ones. Currently this goes up to compatibility with freeciv master commit ??????, ??-???-17.
Capability string of each ruleset file must be changed. Also a new format_version field needs to be added. For 3.1 rulesets the format version is 20.
[datafile] options="+Freeciv-ruleset-Devel-2017.Jan.02" format_version=20