[Clipboard API] setData description

[João Eiras]

Hi.
The description for DataTransfer.setData [1] says: "Calling setData() from  
a paste event handler must not modify the data that is inserted, and must  
not modify the data on the clipboard."

That second phrase is very confusing. Isn't it the objective of listening  
to cut/copy events, to possibly prevent the default action and set the  
data calling setData, therefore changing clipboard contents ?

Thank you.

[1]  
http://dev.w3.org/2006/webapi/clipops/clipops.html#widl-clipboardData-setData-boolean-DOMString-type-DOMString-data