[Seaside] Usage of Canvas' #select and #labels

[Rick Flower]

Philippe Marschall wrote:

> html select
>    beOptional
>    list: orgs;
>    on: #orgId of: self;
>     "You can use #name if you implement #value in Symbol
>     You can leave this out of you implement #displayString or
> #renderOn. in your domain class"
>    labels: [:org | org name ];
>    optionalLabel: 'Select One...'.


Hmm.. I saw the "beOptional" but wasn't sure what it did -- is that just 
a flag that controls whether or not to use the optionalLabel or does it 
do something else as well? I did miss however the #optionalLabel: 
method.  I'm not really sure what the #on: is doing -- it looks like an 
alternative to #callback -- any comments on why its better?  Is that 
because I'm not specifying a #selected call and this one call does both?