r *msg, ...)</code> is not normally called
     directly from an <code class="function">ereport</code> message site; rather it is used
     in <code class="literal">error_context_stack</code> callback functions to provide
     information about the context in which an error occurred, such as the
     current location in a PL function.
     The message string is processed in just the same way as for
     <code class="function">errmsg</code>.  Unlike the other auxiliary functions, this can
     be called more