Documentation needed in ConfigEntityDependency::getDependencies() to explain what the $type == module code is doing

Problem/Motivation

The class Drupal\Core\Config\Entity\ConfigEntityDependency contains some confusing code in its getDependencies() method:

  /**
   * Gets the configuration entity's dependencies of the supplied type.
   *
   * @param string $type
   *   The type of dependency to return. Either 'module', 'theme', 'config' or
   *   'content'.
   *
   * @return array
   *   The list of dependencies of the supplied type.
   */
  public function getDependencies($type) {
    $dependencies = [];
    if (isset($this->dependencies[$type])) {
      $dependencies = $this->dependencies[$type];
    }
    if ($type == 'module') {
      $dependencies[] = substr($this->name, 0, strpos($this->name, '.'));
    }
    return $dependencies;
  }

The lines of code around if ($type == 'module') need a code comment (see first comment on this issue for more discussion).

Steps to reproduce

Proposed resolution

Add a comment to the code (see comment #1 on this issue).

Remaining tasks

Make a patch.

User interface changes

No

API changes

No

Data model changes

No

Release notes snippet

No