-- A `@书社:cksum` attribute on toplevel result elements, giving the
- `cksum` checksum of the corresponding source file.
+- For toplevel result elements :—
+
+ - A `@书社:cksum` attribute giving the `cksum` checksum of the
+ corresponding source file.
+
+ - A `@书社:mtime` attribute giving the last modified time of the
+ corresponding source file.
+
+ - A `@书社:identifier` attribute giving the ⛩️📰 书社 identifier
+ (i·e, starting with `about:shushe?`) of the corresponding source
+ file.