If ADD is speficied, negative values will reduce the speed.
-------- KEYS --------
<targetname key="targetname" name="targetname">Activating trigger points to this.</targetname>
-<real key="speed" name="speed">Speed value to set (default: 100).</real>
+<real key="speed" name="speed">Speed value to set (default: 100). A value of 0 will be interpreted as such and not as the default value.</real>
-------- SPAWNFLAGS --------
<flag key="PERCENTAGE" name="Percentage" bit="0">value is treated as percentage of current speed</flag>
<flag key="ADD" name="Add" bit="1">adds the speed instead of setting it</flag>