IOCs - What are the built-in device types?

[David Bracey via Tech-talk <tech-talk at aps.anl.gov>]

There are apparently built-in device types that provide various useful data sources:

  #  get the current time-of-day

  field(DTYP, "Soft Timestamp")
  field(INP,  "@%m/%d/%Y %H:%M:%S%z")

  # get the specified environment variable

  field(DTYP, "getenv")
  field(INP, "@ENGINEER")

Where can I find documentation of these built-in DTYP's?