Type Alias Confidence

Confidence: "high" | "moderate" | "low" | "unconfirmed"

Confidence in the validation algorithm we ship for a given document.

high: official source AND mature library agree.
moderate: one official source OR mature library agrees; the other is missing.
low: only community / reverse-engineered source. We validate format only.
unconfirmed: format checked but no algorithm verified. Format-only validation.