I think he is lumping dark pools in with exchanges. Technically there are only 11 registered US equity exchanges and any displayed quote has to be accessible to all market participants under nondiscriminatory terms.<p>Dark pools OTOH tend to have all sorts of gimmicks with respect to whose orders are allowed to match against other orders and under what circumstances. E.g. if I connect to a bank-run dark pool, I may be able to opt out of matching against principal flow from any of the bank&#x27;s prop desks. The matching rules should be described in a dark pool&#x27;s &quot;form ATS&quot; which some dark pools publish (and some don&#x27;t).