Represents a block of code (a succession of multiple expressions). A single block node can hold two expressions: one expression to be evaluated and second expression, which may be another BLOCK. The first node in the block may be of type ARGS, in which case it represents the arguments to the current method. The second node in the block may be of type BLOCK_ARG, in which case it represents an explicit block argument. The result of the block is the last expression evaluated.