** N.B. This is of interest to anybody using raw schematic specifiers with minetest.place_schematic, or setting a -1 probability in a probability list passed to minetest.create_schematic - if you do not fix this, your mod will break! **
Hello modding community,
Those of you who have used the Schematics API probably realize that the way node probabilities work currently are unintuitive and inconsistent: 0 probability means the node is always placed, -1 means it is never placed, but you can't set a -1 probability with a raw schematic specifier, so the node name needs to be ignore instead, etc.
This, however, is going to be fixed with a new Minetest Schematic version. MTS version 1 files can still be used just fine; MTS version 2 files (schematics created as of this patch) cannot be used with older versions, though.
With the change, a value of 0 now means a 0% chance of a node occuring, and a value of 255 now means the node always occurs. -1 is not valid any longer when being passed along to the probability list in minetest.create_schematic, and "ignore" should not be used to signify that a node is never placed at that position when using raw schematic data.
This change may be somewhat inconvenient, but it is done in the modder's best interest.
Just a reminder, upstream Minetest is *unstable*, and the modding API can (and sometimes does) change within the time before an offical release is made.