Function refuse_skipped_validation 

pub fn refuse_skipped_validation<'a>(
    validate: Option<bool>,
    collections: impl IntoIterator<Item = &'a str>,
) -> Option<ApiError>

The validate flag, which is atproto’s own name for the three stances.

The Lexicon specification names three: explicit, where every record must resolve to a known schema and satisfy it; optimistic, where a record is checked when a schema is at hand and stored faithfully when it is not; and skip. The parameter is a tri-state and each state is one of them.

Unset is optimistic, and it is the stance this server takes. true is explicit and is honoured for the one request: a record in a collection this server holds no lexicon for is refused rather than stored.

false skips the schema check, and this server honours it for a collection it holds no lexicon for: there is no check to skip, and the record is stored and reported unknown just as it is when the flag is unset. A collection whose lexicon it holds is read by an index, a clusterer and a canvas that rely on its shape, and a record stored past its own schema is one no reader downstream can rely on. So false naming one of those collections is refused rather than ignored, for the same reason a swap field is: a request whose precondition this server will not meet should say so.