1 files changed, 5 insertions, 3 deletions

diff --git a/cgitrc.5.txt b/cgitrc.5.txt
index 8a0a9c9..ea0bbe7 100644
--- a/cgitrc.5.txt
+++ b/cgitrc.5.txt
@@ -542,9 +542,11 @@ config files, e.g. "repo.desc" becomes "desc".
 FILTER API
 ----------
 about filter::
-        This filter is given no arguments. The about text that is to be
-        filtered is available on standard input and the filtered text is
-        expected on standard output.
+        This filter is given a single parameter: the filename of the source
+        file to filter. The filter can use the filename to determine (for
+        example) the type of syntax to follow when formatting the readme file.
+        The about text that is to be filtered is available on standard input
+        and the filtered text is expected on standard output.
 
 commit filter::
         This filter is given no arguments. The commit message text that is to