PIF File Timing Point Type

[SimonAlexander]

The PIF File has a "Timing Point Type" entry in the LOC records. The options are "T" (TRUST), "M" (Mandatory) and "O" (Optional)

I get the concept that M and O determine whether they are mandatory or optional timing points in a schedule. Are "T" locations effectively mandatory, and also mandatory reporting points for TRUST? Or are they locations that TRUST uses but ambiguous as to whether they're mandatory or optional? Or something else?