Running trap

I have heard that a "running trap" wasn't allowed, but when I tried to look up a code citation I couldn't find anything. About all it says is that traps shall be of a standard design, which is a rather nebulous term. Can anybody shed light on the concept of a running trap? Is it allowed by code? Not allowed by practice? Anything? Thanks

source https://www.inspectorsjournal.com/topic/18978-running-trap/?do=findComment&comment=173409