up to date xform
<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_substitute</td></tr>
-<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>expr= substitution values were added in 2.5.1</td></tr>
+<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>"expr=" substitution values were added in 2.5.1</td></tr>
</table>
<p>The <code class="directive">Substitute</code> directive specifies a
search and replace pattern to apply to the response body.</p>
</div>
<p> When using an <a href="../expr.html">expression</a> for the
- <var>substitution</var>, regular expression backreferencwa must be
+ <var>substitution</var>, regular expression backreferences must be
backslash ('\') escaped as illustrated in the example below:</p>
<div class="example"><h3>Expression Example</h3><pre class="prettyprint lang-config">&lt;Location "/"&gt;
AddOutputFilterByType SUBSTITUTE text/html
&lt;/Location&gt;</pre>
</div>
-
+ <div class="warning"><h3>Expressions and caching</h3>
+ <p>Caution must be exercised when performing substitutions that reference
+ HTTP request headers. Because this module operates after response headers
+ have been sent, the <a href="../expr.html">expression parser</a> cannot add
+ referenced HTTP request headers to the outgoing Vary header. </p>
+ </div>
<p>A common use scenario for <code>mod_substitute</code> is the
situation in which a front-end server proxies requests to a back-end
