[Xy-pic] \newdir

[Michael Barr]

I got an email from a user that said:

in xybarr.tex the line

\newdir_{ (}{{ }*!/-.5em/@_{(}}%

is missing, necessary to make certain hooked arrows with extra space
work correctly. 

He called it a bug.  Now I never claimed to put every arrow type into diagxy (= xybarr, not my name for it) and I admit to understanding \newdir much less well than I would like to, but I cannot get his macro to work.  In fact, if I try to compile a diagram not even using his macro, it stops on a missing number error.  On the other hand, if I comment out his macro then

\documentclass{article}
 \usepackage[barr]{xy}


  % \newdir_{ (}{{ }*!/-.5em/@_{(}}%

\begin{document}


 $$\bfig
\Square/ (->`>`>`>/[A`B`C`D;```]
 \efig$$

\end{document}

compiles fine and produces a hooked arrow.  There is a \newdir{ (}{{ }*!/-.5em/@^{(}}.  Can anyone tell me what is going on here.  What does the underscore in his \newdir mean anyway?  

Michael