In most cases, use of these commands indicates that you are probably better off programming in something like awk or Perl. But occasionally one is committed to sticking with sed, and these commands can enable one to write quite convoluted scripts.
Specify the location of label for branch commands.
In all other respects, a no-op.
substitution since the last input line was read or conditional branch was taken. The label may be omitted, in which case the next cycle is started.