[Xy-pic] code analysis

[P. R. Stanley]

Hi folks
I thought this might be a good way of making a start on xy-pic:

\[\xymatrix @C=3ex @R=0ex{
*{} & *{} & *{} & *{} & *{} & *++[o][F=]{q_5} \ar@(ur,ul)[]_{0, 1} \\
*{} \ar[r] & q_0 \ar[r]^{0, 1}
& q_1  \ar[r]^{0, 1}
& q_2 \ar[r]^{0, 1}
& q_3 \ar[ru]_0  \ar[rd]_1 \\
*{} & *{} & *{} & *{} & *{} & *++[o][F-]{q_6} \ar@(dr,dl)[]^{0, 1} \\
}\]

I've a rough idea what's described here. the \ar command, for 
example, draws an arrow and by virtue of the "^" command "0, 1" are 
printed over the arrow. The "&" presumably has the same role as in 
the tabular environment. however, there still remains a lot that I 
don't understand in the above code: *{}, *++, to name but two 
commands. Any help to understand the syntax would be appreciated.
Incidentally, in case you're wonderin why I'm not simply compiling 
the code and experimenting with each command to see what it does, is 
because I'm registered blind and screen readers have yet a long way 
to go before they can describe pictures.
Many thanks,
Paul