DoWhitediff performs a [whitediff] comparision on the two input readers.

Ellen (an abbreviation of checker in hungarian) checker is used by [mester], [bíró] systems.

Noop doesn't perform any checking.

TaskYAML checker format is used by CMS as described in the CMS documentation's [Checker] and [Standard manager output] sections.

Testlib is [polygon]'s default checker format [polygon]: https://polygon.codeforces.com.

Whitediff is the [default checker] built into CMS [default checker]: https://cms.readthedocs.io/en/v1.4/Task%20types.html#tasktypes-white-diff.