diff --git a/ChangeLog b/ChangeLog
index 0e61d7ccc6..855dd70cfd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Mon Jul 20 20:35:55 2009  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* io.c (rb_f_open): add rdoc about specifying ext_enc as *-bom.
+
 Mon Jul 20 19:00:58 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* compile.c (compile_dstr_fragments): reduced needless literal.
diff --git a/io.c b/io.c
index 44f79a735f..d9fd157446 100644
--- a/io.c
+++ b/io.c
@@ -5467,6 +5467,9 @@ check_pipe_command(VALUE filename_or_command)
  *  read string will be tagged by the encoding in reading,
  *  and output string will be converted
  *  to the specified encoding in writing.
+ *  If ext_enc ends with '-bom', check whether the input has a BOM. If
+ *  there is a BOM, strip it and set external encoding as
+ *  what the BOM tells. If there is no BOM, use ext_enc without '-bom'.
  *  If two encoding names,
  *  ext_enc and int_enc (external encoding and internal encoding),
  *  are specified, the read string is converted from ext_enc