\xymatrixcolsep is not recognized

[pbelmans]

When parsing the example

$$
\xymatrixcolsep{4pc}
\xymatrix{
(w'', a'', b'', \phi'')
\rtwocell^{(k'_1, \alpha'_1, \beta'_1)}_{(k'_2, \alpha'_2, \beta'_2)}{\delta'}
&
(w', a', b', \phi')
\rtwocell^{(k_1, \alpha_1, \beta_1)}_{(k_2, \alpha_2, \beta_2)}{\delta}
&
(w, a, b, \phi)
}
$$

MathJax throws an "undefined control sequence \xymatrixcolsep".

[sonoisa]

I'm sorry. This command is not implemented yet.
Please use @C as an alternative option.
e.g. \xymatrix @C=4pc { ... }.

current implementation status: http://sonoisa.github.com/xyjax/xyjax.html#ToDo