Where does the mic connect on a TRS headphone connector

[jaydnul]

So this headset has stereo sound and a mic, but the connector only has a tip ring and sleeve. So which part of the connector is for each. (tip for left channel, ring for right channel, sleeve for common, so where does the mic connect.)

 

[berkeman]

So this headset has stereo sound and a mic, but the connector only has a tip ring and sleeve. So which part of the connector is for each. (tip for left channel, ring for right channel, sleeve for common, so where does the mic connect.)

Maybe post a datasheet?