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[SLUG] Clearing a text entry field

Does anyone know a key sequence to empty a text entry field in X applications?  
In particular, I'm thinking of the URL entry field in Netscape/Opera/Mozilla.

I realise I can highlight the text in the field by double clicking, then press 
Delete, but the problem with that is that it changes what's in the clipboard 
and the reason I'm trying to clear the field is to paste what's currently in 
there (for example, a URL from an e-mail I've received).

Thanks in advance,

Harry O.