[0,0]). This always corresponds to a
[hop], e.g., [1,2] is the same as [drr] and
[-2,0] is the same as [uu].
"1,1".
\xymatrix{ A \\
B & C \ar@<1ex>[ul]
\ar@<1ex>[ul];[] }
typesets

i.e., the second \ar[ul] arrow starts at the [ul] entry and ends
in the current entry.