content tests are three-valued: unknown when unreadable or read in part

1 files changed, 7 insertions, 0 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 78dbcd8..5c4c0bd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,13 @@
   on (a self-extracting installer) has no content, like an image: it no
   longer matches a content test, is not set aside by a content exclude, and
   raises no warning.
+- A content test that cannot read its file is unknown rather than false,
+  and `and`/`or`/`not` combine unknowns by three-valued logic. A rule never
+  matches on an unknown, so `(not (content "x"))` no longer acts on a file
+  krino could not read; an exclude holds on an unknown only when the text
+  could change its answer; `explain` shows `?`. A document read only in part
+  answers the keywords found in what was read, and leaves the others
+  unknown.
 - `{1}` … `{9}` keep the name's diacritics: a folded `name` test still
   matches `Lodz`, but `Łódź-faktura.pdf` now files under `Łódź`, not `Lodz`.
 - A tool's error message is shown even when it writes more than the