input pgf.texrelax%
usepgfmodule{oo}relax%
pgfooclass{A}{attribute a=1;}%
bye

wlog{watch: csname pgfooYpgfoo@classname .@pgfoo@process@attributesendcsname}%

! Undefined control sequence.
pgfooYsignal.@pgfoo@process@attributes ...ute@op
                                                  {emitter}pgfooYsignal@emi...
<inserted text>
                }endwrite
pgfoo@inherit@attributes ...ttributesendcsname }

pgfooclass@ ...methods pgfoo@inherit@attributes
                                                  expandafter let csname ...
l.837 }