[linux-audio-dev] a question re: the MIDI spec

Greetings: I'm doing some research for an article about Linux MIDI support. In my text I briefly describe the evolution of the MIDI specification since its adoption, mentioning things like MIDI Time Code, MMC, the sample dump standard, and the standard MIDI file. However, one item has me a bit mystified. I'm unable to ascertain whether multi-port interfaces are in fact described and supported by the spec. I checked the MMA docs on-line, and I also have the Sciacciaferro/De Furia MIDI Programmers Handbook, but nowhere do those sources indicate explicit support for multi-port hardware. Are multi-port MIDI interfaces vendor-specific solutions or is there actually an extension to the MIDI spec somewhere that I'm just missing ? TIA! Best regards, dp