Message89

When replacing node value by an expression, we could replace
the newlines ('\r', '\n', '\r\n') by <text:line-break/> and
tabs ('\t') by <text:tab/> and following spaces by <text:s/>
if they are inside a valid element like defined in
http://docs.oasis-open.org/office/v1.2/os/OpenDocument-v1.2-os-part1.html#__RefHeading__1415204_253892949
http://docs.oasis-open.org/office/v1.2/os/OpenDocument-v1.2-os-part1.html#__RefHeading__1415206_253892949
http://docs.oasis-open.org/office/v1.2/os/OpenDocument-v1.2-os-part1.html#__RefHeading__1415202_253892949

The function could just return a Genshi Markup instead which
is escaped and replace those characters.