framework/base/Module.php
public function getModule($id, $load = true)
    {
        if (($pos = strpos($id, '/')) !== false) {
            // sub-module
            $module = $this->getModule(substr($id, 0, $pos));

            return $module === null ? null : $module->getModule(substr($id, $pos + 1), $load);
        }

        if (isset($this->_modules[$id])) {
            if ($this->_modules[$id] instanceof self) {
                return $this->_modules[$id];
            } elseif ($load) {
                Yii::debug("Loading module: $id", __METHOD__);
                /* @var $module Module */
                $module = Yii::createObject($this->_modules[$id], [$id, $this]);
                $module->setInstance($module);
                return $this->_modules[$id] = $module;
            }
        }

        return null;
    }
public function getModule($id, $load = true)
    {
        if (($pos = strpos($id, '/')) !== false) {
            // sub-module
            $module = $this->getModule(substr($id, 0, $pos));

            return $module === null ? null : $module->getModule(substr($id, $pos + 1), $load);
        }

        if (isset($this->_modules[$id])) {
            if ($this->_modules[$id] instanceof self) {
                return $this->_modules[$id];
            } elseif ($load) {
                Yii::debug("Loading module: $id", __METHOD__);
                /* @var $module Module */
                $module = Yii::createObject($this->_modules[$id], [$id, $this]);
                $module->setInstance($module);
                return $this->_modules[$id] = $module;
            }
        }

        return null;
    }
Retrieves the child module of the specified ID.
This method supports retrieving both child modules and grand child modules.
@param string $id module ID (case-sensitive). To retrieve grand child modules,
use ID path relative to this module (e.g. `admin/content`).
@param bool $load whether to load the module if it is not yet loaded.
@return Module|null the module instance, `null` if the module does not exist.
@see hasModule()