Explain more why pragma is the best fit

[domenic]

@erights, @mikesamuel, and @waldemarhorwat all had points I will try to jot down:

• Pragmas offer a unique syntactic space in that they are lexical and they are backward-compatible
• Tooling (e.g. an inliner) that wants to treat censored functions differently requires lexical source code information, not runtime information. (Compare to .censor() alternative.)
• ... I forget Waldemar's point :(

[mikesamuel]

+1

I would like to avoid inliners having to use heuristics to decide whether they can inline a call to a potentially censored function into a potentially uncensored function's body.