plan 10: a format with no text is no match, not unreadable

1 files changed, 5 insertions, 2 deletions

diff --git a/docs/design.md b/docs/design.md
index 5b70183..a232baf 100644
--- a/docs/design.md
+++ b/docs/design.md
@@ -202,7 +202,9 @@ no rule has run yet, `(matched)` is never true inside an exclude.
 An exclude fails closed: when evaluating it reaches a content test that
 cannot read the file (over `max-read`, a tool missing, failing or timing
 out), the exclude holds, and the file is set aside as "(content
-unreadable)" with the warning. An exclude protects files, so a file krino
+unreadable)" with the warning. A file whose format has no text at all (an
+image, an archive) is not unreadable: it contains no keyword, so its
+content tests are simply false and raise no warning. An exclude protects files, so a file krino
 could not check is left alone. Mistakes in krino.conf's excludes are
 reported even while no directory is included.
 
@@ -255,7 +257,8 @@ UTF-8 is replaced by U+FFFD before folding.
    `path`, then `duplicate`, then `content`. Content is extracted at most once per file,
    and only if evaluation reaches a `content` test.
 4. If a file's text cannot be extracted, `content` is false and the plan
-   shows a warning naming the rule that wanted it. Inside an `exclude` the
+   shows a warning naming the rule that wanted it. A format with no text
+   (§6, "anything else") is not a failure: `content` is false, silently. Inside an `exclude` the
    whole exclude then holds instead (§4.6).
 
 ### 5.5 Duplicates