I just got a new job and am working with several websites made with WordPress. Looking at the code, it's obvious that there has been at least a few different coders at work. Some pages are straightforward - I can find all of the source code in the "Pages" tab. But with other pages, I can follow the source code down the page, then the code (on the "Pages" tab) ends, and there's still more content on the website (like whole paragraphs and images and whatnot, not just a footer).
On one page I managed to find the source inside a "frame.php" file under Appearance > Editor. Still don't know how the page took the code from the file, but I know that when I edited the frame.php file, the content on the website changed.
What are some common (and uncommon) places where simple content code (like text) can be hiding?