Unfortunately some of us still have to support complex legacy apps that are running a business.
If your legacy project is running on Symfony 1.* then you should know (or you know already) that documentation for Symfony 1.* API is gone. It was available here http://www.symfony-project.org/api/ but it’s currently redirecting to the legacy documentation, not the API.
The API documentation was a developer savior, because you no more can find a useful information in the internet for the 1.* version.
Also you can scrape content from Wayback Machine using tool - https://github.com/hartator/wayback-machine-downloader
For 1_4 version I have already downloaded and uploaded pages to github - https://github.com/c0d3b0t/symfony_1_4_api_docs
You can download and run it on some web server, or simply run it with
php -S localhost:8000
Happy coding! And always Upgrade! :)