syntax question

[Ray Andrews <rayandrews@xxxxxxxxxxx>]

${${(z)string}[1]}

... that does what I expect, and it's readable, however I'm curious why 
this does not say the same thing:

${(z)string[1]}

... How can that mean anything different?  It seems to just sorta get to 
the point more quickly and given the " (z) " it seem unintuitive that it 
would only print the first character just as:

${string[1]}

... does.  So in the second line the " (z) " seems to do nothing.  I'd 
expect the first two lines to be semantically the same and the third 
line to be a single character.  Is this explainable?  I know it's a 
nit-pick but I'd like to understand it.