PageService.php
private function getPageId()
    {
        if (preg_match('/\/page\/(\w+)$/', $this->name, $matches)) {
            $id = $matches[1];
        } else {
            $id = $this->environment->getRequestHelper()->getIdentifierParam('id', null, true);
        }
        return $id;
    }
private function getPageId()
    {
        if (preg_match('/\/page\/(\w+)$/', $this->name, $matches)) {
            $id = $matches[1];
        } else {
            $id = $this->environment->getRequestHelper()->getIdentifierParam('id', null, true);
        }
        return $id;
    }
Checks if the page is contained in service name or specified in parameter 'id' and returns the value then.

@return mixed