I fear that doesn't even work with ordinary USASCII input. I tweaked 
readKeyboard to simulate additional characters arriving in close succession:

         self hasSelection ifTrue: "save highlighted characters"
             [UndoSelection := self selection].
*((model isKindOf: Workspace) and: [char = $z]) ifTrue: [typeAhead 
nextPutAll: '123'].*

         self zapSelectionWithCompositionWith: typeAhead contents.

and what I get by typing some z's in a Workspace is:

z123zzzzzz123123123123123123

I think the safest way to guard against multiple characters arriving in 
quick succession is to simply process each one completely before 
proceeding to the next. This, after all, is the likeliest case by far 
for modern computers and ordinary humans typing:

         self deselect.
*sensor keyboardPressed ifTrue: "was a whileTrue:"*
             [char := sensor keyboardPeek.
             (self dispatchOnCharacter: char with: typeAhead) ifTrue:
                 [self doneTyping.
                 self setEmphasisHere.
                 ^self selectAndScroll; updateMarker].
             self openTypeIn].

Cheers,
Bob

On 2/9/13 1:01 AM, commits at source.squeak.org wrote:
> aText := Text string: newString emphasis: emphasisHere.
> - 	self markBlock < self pointBlock
> - 		ifTrue: [self setMark: self markBlock stringIndex - 1]
> - 		ifFalse: [self setPoint: self  pointBlock stringIndex - 1].
> -
>    	wasComposition := true.
> + 	self markBlock < self pointBlock
> + 		ifTrue: [ self setMark: self markBlock stringIndex - 1.
> + 				self zapSelectionWith: aText.
> + 				self setMark: self markBlock stringIndex + 1]
> + 		ifFalse: [ self setPoint: self pointBlock stringIndex - 1.
> + 				self zapSelectionWith: aText.
> + 				self setPoint: self pointBlock stringIndex + 1]
> - 	self zapSelectionWith: aText.

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