In cricket, how far along the crease is a non-striker allowed to stand to the right or left?
Could they stand at the boundary and still be in their ground, or is there a limit to the "width" of the crease?
It is impossible to stand outside the crease to the left or right, as the crease is of unlimited length; quoting from Law 7.3 The popping crease:
The popping crease [...] shall be considered to be unlimited in length.
Other than taking a position which would obstruct the fielding side, there is no restriction in the Laws as to where the non-striker may stand.
The non striker can stay and can start only in pitch zone, he can not start standing in infield or outfield.