Improved sections doc for Bug: 58789

containers apply enclosed configuration directives only

to sites accessed through <module>mod_proxy</module>'s proxy server

that match the specified URL. For example, the following configuration

will prevent the proxy server from being used to access the

<code>www.example.com</code> website.</p>

will allow only a subset of clients to access the

<code>www.example.com</code> website using the proxy server:</p>

<highlight language="config">

<Proxy "http://www.example.com/*">

    Require all granted

    Require host yournetwork.example.com

</Proxy>

</highlight>

</section>

    type="section">Directory</directive> container in the processing

    order.</p>

    <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>

    <note><title>Technical Note</title>

      There is actually a

      <code>&lt;Location&gt;</code>/<code>&lt;LocationMatch&gt;</code>

      completed.

    </note>

<section id="merge-examples"><title>Some Examples</title>

<section id="relationship-module-configuration"><title>Relationship between modules and configuration sections</title>

    <p>One question that often arises after reading how configuration sections are

    merged is related to how and when directives of specific modules like <module>mod_rewrite</module>

    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 

        <directive module="mod_headers">Header</directive> directive of <module>mod_headers</module> to set

        a specific HTTP header. What value will httpd set in the <code>CustomHeaderName</code> header for a request to

        <code>/example/index.html</code> ?

    </p>

    <highlight language="config">

<Directory "/">

    Header set CustomHeaderName one

    <FilesMatch ".*">

        Header set CustomHeaderName three

    </FilesMatch>

</Directory>

<Directory "/example">

    Header set CustomHeaderName two

</Directory>

    </highlight>    

    <ul>

        <li><directive>Directory</directive> "/" matches and an initial configuration to set the <code>CustomHeaderName</code> header with the value <code>one</code> is created.</li>

        <li><directive>Directory</directive> "/example" matches, and since <module>mod_headers</module> specifies in its code to override in case of a merge, a new configuration is created to set the <code>CustomHeaderName</code> header with the value <code>two</code>.</li>

        <li><directive>FilesMatch</directive> ".*" matches and another merge opportunity arises, causing the <code>CustomHeaderName</code> header to be set with the value <code>three</code>.</li>

        <li>Eventually during the next steps of the HTTP request processing <module>mod_headers</module> will be called and it will receive the configuration to set the <code>CustomHeaderName</code> header with the value <code>three</code>. <module>mod_headers</module> 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 <directive>Directory</directive> in the merge order. The important concept to understand is that configuration sections like  <directive>Directory</directive> and <directive>FilesMatch</directive> are not comparable to module specific directives like <directive module="mod_headers">Header</directive> or <directive module="mod_rewrite">RewriteRule</directive> because they operate on different levels.

    </p>

</section>

<section id="merge-examples"><title>Some useful examples</title>

<p>Below is an artificial example to show the order of

merging. Assuming they all apply to the request, the directives in

</highlight>

<p>For a more concrete example, consider the following.  Regardless of

any access restrictions placed in <directive module="core"

type="section">Directory</directive> sections, the <directive