cleanup, docs

site/doc/pages/file_mtime.txt

@@ -1,16 +1,18 @@
 :sig
-time_t file_mtime(String file_name)
+u64 file_mtime(String file_name)
 
 :params
-file_name : name of the file
-return value : Unix time stamp of the file's last modification
+file_name : path to inspect, resolved against the unit's directory
+return value : last-modified time as a Unix timestamp, or 0 if missing
+
+:content
+Returns a file's last-modified time as a Unix timestamp. Compare two files' mtimes for cache-freshness checks, or test for `> 0` to confirm a file exists with a real timestamp.
+
+:example
+file_put_contents("/tmp/doc-mtime.txt", "x");
+print(file_mtime("/tmp/doc-mtime.txt") > 0 ? "has a modification time" : "missing", "\n");
 
 :see
 >sys
->time
-
-:content
-Retrieves the last modification date of `file_name` as a Unix timestamp.
-
-:example
-print("file_mtime example\n");
+file_stat
+time