Function: next
Section: programming/control
C-Name: next0
Prototype: D1,L,
Help: next({n=1}): interrupt execution of current instruction sequence, and
 start another iteration from the n-th innermost enclosing loops.
Doc: interrupts execution of current $seq$,
 resume the next iteration of the innermost enclosing loop, within the
 current function call (or top level loop). If $n$ is specified, resume at
 the $n$-th enclosing loop. If $n$ is bigger than the number of enclosing
 loops, all enclosing loops are exited.
