There seem to be some issues with l3messages.  I tried to set up some
messages using \err_interrupt_new:NNNnnn.  Running this, I first get an
undefined \NamesStart:, which should of course be \NamesStart.  A quick
\let:NN then gives me undefined \int_while:nNnT.  I think that is fixed
with \let:NN\int_while:nNnT\int_whiledo:nNnT, but my error still looks a
little odd.  For example:

\err_interrupt_new:NNNnnn \c_keys_err_tlp \keyunknownerr{1}


! The key `/test/key three' is unknown
and is being ignored.
\err_display_aux:w ...wline: and is being ignored}

l.16 \keys_manage:n{/text/key~three}


Notice the odd line \err_diplay ... Have I missed something here?
Joseph Wright