December 25th Tuesday (十二月 二十五日 火曜日)

  The APLOG_TOCLIENT is valid only in ap_log_rerror(), and cause logger to set an entry in the request notes. 
Thus a handler can retrieve an error message using

  errmsg = apr_table_get(r->notes, "error-notes");

and report the exact error message back to the browser.  (Note that errmsg must be escaped if it appears in
an HTML or XML response.)