hello,

> SoupTag>>doesNotUnderstand: aMessage
>     (aMessage arguments size = 0)
>         ifFalse: [^ super doesNotUnderstand: aMessage].
>     ^ attributes
>         at: aMessage selector
>         ifAbsent: [super doesNotUnderstand: aMessage]

this can be simpler, since the dictionary lookup will not confuse #id 
with #id:, so you can get rid of the arguments size test:

SoupTag>>doesNotUnderstand: aMessage
      ^ attributes
          at: aMessage selector
          ifAbsent: [super doesNotUnderstand: aMessage]

> SoupTag>>find: aBlock
>     [(aBlock value: self) ifTrue: [^ self]]
>         on: MessageNotUnderstood
>         do: [:e | e resume: false].
>     children do:
>         [:anElement |
>         | found |
>         found := anElement find: aBlock.
>         found ifNotNil: [^ found]].
>     ^ nil
> 

if there is only one element to be found, the order in which you search 
for it does not matter. so you can start by scanning the children, which 
makes it possible to write a simple recursive method:

SoupTag>>find: aBlock

      ^ children detect: [:anElement | (anElement find: aBlock) notNil]
	ifNone: [
	  [(aBlock value: self) ifTrue: [self]]
         	 on: MessageNotUnderstood
          	 do: [nil]].


now I must say your overall design seems to me very complex and really 
overusing the DNU mechanism. it should be possible to do what you want 
in a much simpler way, but since I don't know what you want to implement 
exactly I will not elaborate on this.

regards,


Stef