A small word about the defined subsets:
The supported list of elements was getting rather large so the list is divided into "subsets".

This is to provide a way for a levelcreator or toolcreator to know what kind of elements should be supported, depending on what game engine the level or tool is meant for.

a subset is related to a game engine, but is not the same.
For example: the original Emerald Mine engine uses SOME of the BD-subset elements and ADDS ALL of the EM-subset elements.
An element is linked to the subset where it was first used.

Currently the followinf subsets are defined:

BD	BoulderDash	All elements from the "official" First Star Boulderdash games - up to the BoulderDash Construction Kit
BDex	BoulderDash extended	All elements that where added after the official games. (In engines like 1stB and CrLi )
BDin	BoulderDash internal	All elements that should not be used directly in levelmaps, but have a different purpose, e.g. for use with Diego effects
EM	Emerald Mines	All elements from the "official" Kingsoft Emerald Mines games. (used in Emerald Mines 1,2 and 3)
EMC	Emerald Mines Club	All elements added by No One Inc / Ruppelware as released in the V5 and V6 engines of the Emerald Mine Club
SP	Supaplex	All elements of the game Suppaplex
SO	Sokobal	All elements of the game Sokoban
DC	Diamond Caves	All elements added by the Diamond Caves series (1, 2 and 3)
RnD	Rocks'n'Diamonds	All elements added by the game Rocks'n'Diamonds
DX	DX-Boulderdash	All elements added by the game DX-Boulderdash