diff --git a/docs/manual/mod/mod_proxy.xml b/docs/manual/mod/mod_proxy.xml
index 53efc1c479..9ed55f6edf 100644
--- a/docs/manual/mod/mod_proxy.xml
+++ b/docs/manual/mod/mod_proxy.xml
@@ -1559,9 +1559,25 @@ proxied server</description>
     match the proxy, you must load and enable <module>mod_proxy_html</module>.
     </p>
 
-    <p><var>path</var> is the name of a local virtual path; <var>url</var> is a
-    partial URL for the remote server. These parameters are used the same way as
-    for the <directive module="mod_proxy">ProxyPass</directive> directive.</p>
+    <p><var>path</var> is the name of a local virtual path. It is combined 
+    with the requests scheme, host, and port to form the replacement 
+    prefix of the affected response header.  
+    This parameter is usually the same as the first parameter of the 
+    <directive module="mod_proxy">ProxyPass</directive> directive.
+    </p>
+
+    <p><var>url</var> is a partial URL for the remote server. When the remote
+    server sends the specifically mentioned headers beginning with this partial
+    URL, the prefix from the remote server is replaced with a prefix that
+    points to the reverse proxy.
+    This parameter is usually the same as the second parameter of the 
+    <directive module="mod_proxy">ProxyPass</directive> directive, but it may
+    differ if the remote server uses a different scheme, host, port, or path
+    in the affected headers.  In configurations with 
+    <directive module="mod_proxy">ProxyPreserveHost</directive>, the hostname
+    in the partial URL may already be the hostname of the reverse proxy, which
+    will prevent the matching and replacement done by this directive.
+    </p>
 
     <p>For example, suppose the local server has address
     <code>http://example.com/</code>; then</p>