[MEI-L] Key change encoding in orchestral scores

[drizo at dlsi.ua.es]

Dear MEI List,

when we encode a staff with staves containing transposing instruments we use (using pseudo-xml):

<scoreDef NO-KEY-SPECIFICATION-HERE>
 <staffDef NO-TRANSPOSING-INSTRUMENT key.mode= "major" key.sig= "4f">
 <staffDef CLARINET-IN-E♭ key.mode= "major" key.sig= "1f" trans.diat= "2" trans.semi= "3">
</scoreDef>

How should we encode a key change in the middle of the piece? I see that scoreDef may contain @trans.* 
attributes, but as scoreDef is not inside a <staff> element, I don't know how to set the different key 
signatures to a different staves. 

I could encode scoreDef without trans.diat and trans.semi and use the trans.diat defined in staffDef to adapt 
the "sounded key" to the "written key". 

Best,
David