The accessor getMF1Functions() is replaced with a static MF1Functions, which contains an expanded set of MF1 compatibility functions; most of these wrap default or draft MF2 spec functions.

A validator mf1Validate() is provided. This is not run during mf1ToMessage(), though, as the functions now validate their options at runtime (this provides for better fallback).

MF1 syntax support is extended, so datetime & number skeletons + number patterns are now supported. As the MF2 option bags do not provide all of the same features, a best effort is made to match the input. The number format scale/dddd token is specifically supported, however, as it's often required for percentage formatting.