[Enhancement] Should these API's be marked with the [Pure] attribute

[Smurf-IV]

TLDR:
Indicates that a type or method is pure, that is, it does not make any visible state changes.

See https://docs.microsoft.com/en-us/dotnet/api/system.diagnostics.contracts.pureattribute?view=netframework-4.8

[ndrwrbgs]

For any that do not take a delegate, this would be okay. Those that do though have their purity implicit on the purity of the delegate, so would need to be omitted.
Do you want to send a PR adding it, Smurf?

[Smurf-IV]

I've been trying to set-up seperate PR's but they keep being merged into the single outstanding one, so I gave up, and just Commented each with a relevant comment.
I'll wait until the Existing PR "Goes away"