The ▶Rad command is used to convert both degrees and gradians into radians. (If the command is given a value in radians it returns that value unchanged).
If you do not specify what unit you want to be used (using either the r command, the ° command, or the G command), whatever default the calculator's mode is set to will be used. Here are some examples:
:setMode("ANGLE", "DEGREE") :90▶Rad 1 :90^r▶Rad 90
It appears to be equivalent to the r command, but only on the TI-89 Titanium or Voyage 200.