diff --git a/reference/pcre/pattern.modifiers.xml b/reference/pcre/pattern.modifiers.xml
index c17233c57d..4f1c4c3b52 100644
--- a/reference/pcre/pattern.modifiers.xml
+++ b/reference/pcre/pattern.modifiers.xml
@@ -251,10 +251,16 @@ $html = preg_replace_callback(
       <listitem>
        <simpara>
         This modifier turns on additional functionality of PCRE that
-        is incompatible with Perl. Pattern strings are treated as
-        UTF-8. This modifier is available from PHP 4.1.0 or greater
-        on Unix and from PHP 4.2.3 on win32.
-        UTF-8 validity of the pattern is checked since PHP 4.3.5.
+        is incompatible with Perl. Pattern and subject strings are
+        treated as UTF-8. This modifier is available from PHP 4.1.0
+        or greater on Unix and from PHP 4.2.3 on win32. UTF-8
+        validity of the pattern and the subject is checked since PHP
+        4.3.5. An invalid subject will cause the preg_* function to
+        match nothing; an invalid pattern will trigger an error of
+        level E_WARNING. Five and six octet UTF-8 sequences are
+        regarded as invalid since PHP 5.3.4 (resp. PCRE 7.3
+        2007-08-28); formerly those have been regarded as valid
+        UTF-8. 
        </simpara>
       </listitem>
      </varlistentry>