Custom world generation/processor


 * The root tag
 * : A list of processors
 * : Can be or
 * If is :
 * : A number between 0 and 1
 * If is :
 * : A list of rules to apply from top to bottom
 * : The block that is placed if all conditions are met; see.
 * (string): ID of the block
 * : Block states
 * (string): A block state key and its value.
 * : The block that is placed if all conditions are met; see.
 * (string): ID of the block
 * : Block states
 * (string): A block state key and its value.
 * (string): A block state key and its value.