Takes a block and queues a newgroup that is indented 1 level further.
# File lib/prettyprint.rb, line 260
def group_sub
group = Group.new(@group_stack.last.depth + 1)
@group_stack.push group
@group_queue.enq group
begin
yield
ensure
@group_stack.pop
if group.breakables.empty?
@group_queue.delete group
end
end
end