the absheight option should only be used for ores that should appear in mountains. It forces an ore that occurs in a negative range to also -appear in the corresponding positive range.
+appear in the corresponding positive range. Another confusing parameter +of the register_ore function is y_min. +Most programmers are more concerned with y_max, which is how deep a +player must dig to have a chance of mining the ore. +y_min is the value below which the +ore stops. Sometimes people set this to a very low number that normally +won't be reached, such as -31000. This number may be useful for certain +cases where an ore shouldn't occur below a certain point, such as amber +(all nodes generated in this way are called ores in Minetest even if +they are not technically a metal or mineral ore and even if they +cannot be smelted nor drop a mineral--they still use the +minetest.register_ore function).