diff --git a/.hyperhive/review-classifier.yml b/.hyperhive/review-classifier.yml
index 2070c1ea..bb5f5fa2 100644
--- a/.hyperhive/review-classifier.yml
+++ b/.hyperhive/review-classifier.yml
@@ -34,14 +34,24 @@ classifications:
   - name: tests-with-behaviour
     description: >-
       Every change to how the code behaves comes with a new or updated test
-      that exercises it.
+      that exercises it. A diff whose changed files are all test code
+      (a fixture under `nix/module-eval/`, `nix/checks.nix`, a crate's
+      `tests/` directory, or Rust inside `#[cfg(test)]` or a `#[test]`
+      function) changes no behaviour: the question is not applicable. A PR
+      that changes behaviour and tests together matches.
     polarity: positive
     threshold: 65
   - name: docs-updated
     description: >-
       A change to what an operator or user sees, such as a command, flag,
       option, endpoint, service or default, updates the matching page under
-      docs/ or the crate's README in the same diff.
+      docs/ or the crate's README in the same diff. For a nix option whose
+      own default, type or meaning changes, an updated `description` on that
+      option counts as the documentation. It does not cover a change in what
+      a service does for operators across hosts, such as what it scrapes,
+      serves or publishes: that needs a docs/ page or README. A nix option
+      declared `internal = true` or `visible = false` is not something an
+      operator sees, so adding or changing one needs none of these.
     polarity: positive
     threshold: 65
   - name: one-purpose