src/PEAR/Config.php
function setRegistry(&$reg, $layer = 'user')
    {
        if ($this->_noRegistry) {
            return false;
        }

        if (!in_array($layer, array('user', 'system'))) {
            return false;
        }

        $this->_registry[$layer] = &$reg;
        if (is_object($reg)) {
            $this->_registry[$layer]->setConfig($this, false);
        }

        return true;
    }
function setRegistry(&$reg, $layer = 'user')
    {
        if ($this->_noRegistry) {
            return false;
        }

        if (!in_array($layer, array('user', 'system'))) {
            return false;
        }

        $this->_registry[$layer] = &$reg;
        if (is_object($reg)) {
            $this->_registry[$layer]->setConfig($this, false);
        }

        return true;
    }
This is to allow customization like the use of installroot
@param PEAR_Registry
@return bool