Setting the output encoding in REXML

I'm sure this is really obvious, but I can't find it in either the
REXML tutorial or the RDoc. How do I set the encoding for output? I
tried doing this:

doc.xml_decl.encoding = 'ISO-8859-1'

which sets the "encoding" attribute in the declaration correctly. But
it doesn't actually do turn, say, \251 into ©, which is what I
want.

Francis