Composer: What's The Difference Between Require and Autoloader?
<p>I'm just getting started with Composer.  I want to make sure I correctly understand what Composer does when it downloads and installs packages <strong>from Packagist</strong> using Composer's defaults.  Is this correct:</p>

<ol>
<li>The "Require" section of the <code>composer.json</code> file specifies the packages that will be downloaded and installed <strong>from Packagist.</strong>  <em>Only those packages listed in the "Require" section will be downloaded and installed.</em></li>
<li>During the download and install process in Step #1, an <code>autoload_namespaces.php</code> file is created within the default <code>vendor</code> folder (which is created in the root of the project during downloading and installation).  This file contains a namespace definition for each downloaded and installed package which is mapped to a folder on the file system</li>
<li>The classes contained within the files downloaded in Step #1 are only accessible via <code>autoload_namespaces.php's</code> namespaces IF EACH DOWNLOADED FILE CONTAINS A NAMESPACE DEFINITION THAT MATCHES ONE OF <code>autoload_namespaces.php's</code> NAMESPACES.  <strong>If no namespace definition is present within a downloaded file the classes within the file are assigned to the GLOBAL namespace.</strong></li>
<li>The "Autoloader" section of the composer.json file is ONLY used to define custom namespaces and map those custom namespaces to a folder on the file system.  Downloaded and installed package namespaces are defined <strong><em>only in the</em></strong> <code>autoload_namespaces.php</code> <strong><em>file</em></strong> AND ARE NOT AFFECTED IN ANY WAY BY THE "Autoloader" SECTION of <code>composer.json</code>, ASSUMING THAT A NAMESPACE PRESENT WITHIN THE <code>autoload_namespaces.php</code> FILE IS NOT DUPLICATED IN THE <code>composer.json</code> "Autoloader" SECTION.</li>
</ol>

<p>Is my understanding about the above items correct?  If not, would you please correct me?</p>

<p>Thanks In Advance -</p>