Custom world generation/rule test


 * The root tag.
 * Can be, to test for a block,  to test for a specific block state,  to test for a block with a random chance,  to test for a block state with a random chance, or  to test for a block in a block tag.
 * If is, additional fields are as follows :
 * : A block ID.
 * If is, additional fields are as follows :
 * : A block state.
 * If is, additional fields are as follows :
 * : A block ID.
 * : The probability of the predicate to pass if the block is found. Values below 0.0 is treated as 0.0; values above 1.0 is treated as 1.0.
 * If is, additional fields are as follows :
 * : A block state.
 * : The probability of the predicate to pass if the block state is found. Values below 0.0 is treated as 0.0; values above 1.0 is treated as 1.0.
 * If is, additional fields are as follows :
 * : A block tag without.
 * If is, additional fields are as follows :
 * : A block tag without.