Extra TSV adds many convenience types to Sane TSV:

- Timestamps
  Just this format for now: yyyy-MM-ddTHH:mm:ss.ffff
- Timespans
- Time durations
- Multiformats
  - Multihashes
  - Multiprotocols
  - ...
- Physical units
  To start with, just use SI base and derived units
  - Base units
    - m
    - s
    - A
    - K
    - cd
    - mol
    - kg
  - Derived units
    - Hz
    - rad
    - sr
    - N
    - Pa
    - J
    - W
    - C
    - V
    - F
    - Ω
    - S
    - Wb
    - T
    - H
    - °C
    - lm
    - lx
    - Bq
    - Gy
    - Sv
    - kat
  How to handle derived units?