- * already exists, it is truncated down to zero length (an empty file). If
- * @fmode is %filemode_WriteAppend, the file mark is set to the end of the
- * file.
+ * already exists, it is truncated down to zero length (an empty file); the
+ * other modes do not truncate. If @fmode is %filemode_WriteAppend, the file
+ * mark is set to the end of the file.
+ *
+ * <note><para>
+ * Note, again, that this doesn't match stdio's fopen() call very well. See
+ * <link linkend="filemode-WriteAppend">the file mode constants</link>.
+ * </para></note>
+ *
+ * If the filemode requires the file to exist, but the file does not exist,
+ * glk_stream_open_file() returns %NULL.
+ *
+ * The file may be read or written in text or binary mode; this is determined
+ * by the @fileref argument. Similarly, platform-dependent attributes such as
+ * file type are determined by @fileref. See <link
+ * linkend="chimara-File-References">File References</link>.