    public function getSchemeObj($config, $context) {
        $registry = HTMLPurifier_URISchemeRegistry::instance();
        if ($this->scheme !== null) {
            $scheme_obj = $registry->getScheme($this->scheme, $config, $context);
            if (!$scheme_obj) return false; // invalid scheme, clean it out
        } else {
            // no scheme: retrieve the default one
            $def = $config->getDefinition('URI');
            $scheme_obj = $def->getDefaultScheme($config, $context);
            if (!$scheme_obj) {
                // something funky happened to the default scheme object
                trigger_error(
                    'Default scheme object "' . $def->defaultScheme . '" was not readable',
                    E_USER_WARNING
                );
                return false;
            }
        }
        return $scheme_obj;
    }
The software does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.