Begin G-code block.
G-code block is executed as single step. This is often used in cycles and macros.
(block_begin)
G21 G90 G00 X-30 Y-30 G01 X-30 Y30 (block_begin) G01 X30 Y30 G01 X30 Y-30 (block_end) G01 X-30 Y-30
block_end, Single Step