Is Time To Interactive calculated by WPT?

[MachMetrics]

I know Time To Interactive is becoming an important metric, but having a hard time figuring out if this is calculated by WebPageTest or not?

I see the documentation here, but that seems more of a lesson than an explanation for WPT

This thread implies it is being calculated (assuming domInteractive?), yet this thread gives me the impression it's something we need to calculate on our own?

Is it domInteractive or something that's not built in??

Thanks in advance,
Shane