For some facilities in the Second Edition of PNG, there were a number of alternatives defined, and this International Standard allowed other alternatives to be defined by registration. According to the rules for the designation and operation of registration authorities in the ISO/IEC Directives, the ISO and IEC Councils have designated the following as the registration authority:
Email: png-group@w3.org
That specification is now superseded by PNG Third Edition, and issues related to that specification should be raised on GitHub.