container takes the place of the <code class="directive"><a href="./mod/core.html#directory"><Directory></a></code> container in the processing
order.</p>
-<div class="note"><h3>Merge is not always Override</h3>
- <p>Later sections override earlier ones, however each module is responsible
- for interpreting what form this override takes. A later configuration section
- with directives from a given module might cause a conceptual "merge" of some
- directives, all directives, or a complete replacement of the modules
- configuration with the module defaults and directives explicitly listed in
- the later context.</p>
- <p><code class="directive">Directory</code>, <code class="directive">FilesMatch</code>,
- <code class="directive">Location</code> and the other directives discussed in this section
- implement the same merging strategy, namely "override" when applied to the same target.</p>
-</div>
-
-<div class="note"><h3>Technical Note</h3>
+ <div class="note"><h3>Technical Note</h3>
There is actually a
<code><Location></code>/<code><LocationMatch></code>
sequence performed just before the name translation phase
are used to map URLs to filenames). The results of this
sequence are completely thrown away after the translation has
completed.
-</div>
+ </div>
+
+<h3><a name="relationship-module-configuration" id="relationship-module-configuration">Relationship between modules and configuration sections</a></h3>
+ <p>One question that often arises after reading how configuration sections are
+ merged is related to how and when directives of specific modules like <code class="module"><a href="./mod/mod_rewrite.html">mod_rewrite</a></code>
+ are processed. The answer is not trivial and needs a bit of background.
+ Each httpd module manages its own configuration, and each of its directives in httpd.conf specify one piece
+ of configuration in a particular context. httpd does not execute a command as it is read.</p>
+ <p>At runtime, the core of httpd iterates over the defined configuration sections in the order
+ described above to determine which ones apply to the current request. When the first section matches,
+ it is considered the current configuration for this request. If a subsequent section matches too,
+ then each module with a directive in either of the sections is given a chance to merge its configuration between the two sections. The result is a third configuration, and the process goes on until all the configuration sections
+ are evaluated.</p>
+ <p>After the above step, the "real" processing of the HTTP request begins: each module has a chance to run
+ and perform whatever tasks they like. They can retrieve their own final merged configuration from the core
+ of the httpd to determine how they should act.</p>
+ <p>An example can help to visualize the whole process. The following configuration uses the
+ <code class="directive"><a href="./mod/mod_headers.html#header">Header</a></code> directive of <code class="module"><a href="./mod/mod_headers.html">mod_headers</a></code> to set
+ a specific HTTP header. What value will httpd set in the <code>foo</code> header for a request to
+ <code>/example/index.html</code> ?
+ </p>
+ <pre class="prettyprint lang-config"><Directory "/">
+ Header set foo one
+ <FilesMatch ".*">
+ Header set foo three
+ </FilesMatch>
+</Directory>
+
+<Directory "/example">
+ Header set foo two
+</Directory></pre>
+
+ <ul>
+ <li><code class="directive">Directory</code> "/" matches and an initial configuration to set the "foo" header with the value "one" is created.</li>
+ <li><code class="directive">Directory</code> "/example" matches, and since <code class="module"><a href="./mod/mod_headers.html">mod_headers</a></code> specifies in its code to override in case of a merge, a new configuration is created to set the "foo" header with the value "two".</li>
+ <li><code class="directive">FilesMatch</code> ".*" matches and another merge opportunity arises, causing the "foo" header
+ to be set with the value "three".</li>
+ <li>Eventually during the next steps of the HTTP request processing <code class="module"><a href="./mod/mod_headers.html">mod_headers</a></code> will be called and it will receive the configuration to set the "foo" header with the value "three". <code class="module"><a href="./mod/mod_headers.html">mod_headers</a></code> normally uses this configuration to perfom its job, namely setting the foo header. This does not mean that a module can't perform a more complex action like discarding directives because not needed or deprecated, etc..</li>
+ </ul>
+
+ <p>This is true for .htaccess too since they have the same priority as <code class="directive">Directory</code> in the merge order. The important concept to understand is that configuration sections like <code class="directive">Directory</code> and <code class="directive">FilesMatch</code> are not comparable to module specific directives like <code class="directive"><a href="./mod/mod_headers.html#header">Header</a></code> or <code class="directive"><a href="./mod/mod_rewrite.html#rewriterule">RewriteRule</a></code> because they operate on different levels.
+ </p>
-<h3><a name="merge-examples" id="merge-examples">Some Examples</a></h3>
+
+<h3><a name="merge-examples" id="merge-examples">Some useful merge examples to practice</a></h3>
<p>Below is an artificial example to show the order of
merging. Assuming they all apply to the request, the directives in
</Directory></pre>
-<p>Another interesting example is the following one. As described above,
-<code class="directive">FilesMatch</code> is merged after <code class="directive">Directory</code>,
-therefore a request for <code>/var/www/index.html</code> will eventually get the "foo" Header set to
-the value "two", not "three" as somebody might expect from a first look.
-</p>
-
-<pre class="prettyprint lang-config"><Directory "/">
- Header set foo one
- <FilesMatch ".*">
- Header set foo two
- </FilesMatch>
-</Directory>
-
-<Directory "/var/www">
- Header set foo three
-</Directory></pre>
-
-
-<p>The chain of values that the "foo" header will get is: "one", "three" and "two".
-It is important to notice that <code class="directive">Directory</code> and <code class="directive">FilesMatch</code>
-implement the same merging strategy, namely "override" when
-applied to the same path. In this example it means that the last directive applied in the merging order,
-<code class="directive">FilesMatch</code>, sets the final value for the "foo" header.
-</p>
-<p>This is true for .htaccess too, since they have the same priority as <code class="directive">Directory</code>
-in the merging order.</p>
<p>For a more concrete example, consider the following. Regardless of
any access restrictions placed in <code class="directive"><a href="./mod/core.html#directory"><Directory></a></code> sections, the <code class="directive"><a href="./mod/core.html#location"><Location></a></code> section will be
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