framework/web/UrlManager.php
public function parseRequest($request)
    {
        if ($this->enablePrettyUrl) {
            /* @var $rule UrlRule */
            foreach ($this->rules as $rule) {
                $result = $rule->parseRequest($this, $request);
                if (YII_DEBUG) {
                    Yii::debug([
                        'rule' => method_exists($rule, '__toString') ? $rule->__toString() : get_class($rule),
                        'match' => $result !== false,
                        'parent' => null,
                    ], __METHOD__);
                }
                if ($result !== false) {
                    return $result;
                }
            }

            if ($this->enableStrictParsing) {
                return false;
            }

            Yii::debug('No matching URL rules. Using default URL parsing logic.', __METHOD__);

            $suffix = (string) $this->suffix;
            $pathInfo = $request->getPathInfo();
            $normalized = false;
            if ($this->normalizer !== false) {
                $pathInfo = $this->normalizer->normalizePathInfo($pathInfo, $suffix, $normalized);
            }
            if ($suffix !== '' && $pathInfo !== '') {
                $n = strlen($this->suffix);
                if (substr_compare($pathInfo, $this->suffix, -$n, $n) === 0) {
                    $pathInfo = substr($pathInfo, 0, -$n);
                    if ($pathInfo === '') {
                        // suffix alone is not allowed
                        return false;
                    }
                } else {
                    // suffix doesn't match
                    return false;
                }
            }

            if ($normalized) {
                // pathInfo was changed by normalizer - we need also normalize route
                return $this->normalizer->normalizeRoute([$pathInfo, []]);
            }

            return [$pathInfo, []];
        }

        Yii::debug('Pretty URL not enabled. Using default URL parsing logic.', __METHOD__);
        $route = $request->getQueryParam($this->routeParam, '');
        if (is_array($route)) {
            $route = '';
        }

        return [(string) $route, []];
    }
public function parseRequest($request)
    {
        if ($this->enablePrettyUrl) {
            /* @var $rule UrlRule */
            foreach ($this->rules as $rule) {
                $result = $rule->parseRequest($this, $request);
                if (YII_DEBUG) {
                    Yii::debug([
                        'rule' => method_exists($rule, '__toString') ? $rule->__toString() : get_class($rule),
                        'match' => $result !== false,
                        'parent' => null,
                    ], __METHOD__);
                }
                if ($result !== false) {
                    return $result;
                }
            }

            if ($this->enableStrictParsing) {
                return false;
            }

            Yii::debug('No matching URL rules. Using default URL parsing logic.', __METHOD__);

            $suffix = (string) $this->suffix;
            $pathInfo = $request->getPathInfo();
            $normalized = false;
            if ($this->normalizer !== false) {
                $pathInfo = $this->normalizer->normalizePathInfo($pathInfo, $suffix, $normalized);
            }
            if ($suffix !== '' && $pathInfo !== '') {
                $n = strlen($this->suffix);
                if (substr_compare($pathInfo, $this->suffix, -$n, $n) === 0) {
                    $pathInfo = substr($pathInfo, 0, -$n);
                    if ($pathInfo === '') {
                        // suffix alone is not allowed
                        return false;
                    }
                } else {
                    // suffix doesn't match
                    return false;
                }
            }

            if ($normalized) {
                // pathInfo was changed by normalizer - we need also normalize route
                return $this->normalizer->normalizeRoute([$pathInfo, []]);
            }

            return [$pathInfo, []];
        }

        Yii::debug('Pretty URL not enabled. Using default URL parsing logic.', __METHOD__);
        $route = $request->getQueryParam($this->routeParam, '');
        if (is_array($route)) {
            $route = '';
        }

        return [(string) $route, []];
    }
Parses the user request.
@param Request $request the request component
@return array|bool the route and the associated parameters. The latter is always empty
if [[enablePrettyUrl]] is `false`. `false` is returned if the current request cannot be successfully parsed.