Within the edit box in "source" mode, we've added a link suggestion feature that will suggest the names of existing pages and files based on what you type. This is helpful if you cannot remember a precise name to create a link.
How it works
When you start typing a "[[" and then some text, we'll suggest some existing articles that may be what you want to link. The suggestions work in all namespaces. So, for example, if you type "[[File:S " and then some text, we'll suggest existing files on your wiki that start with the letter S.
Disabling the feature
You can dismiss the link suggest box by pressing the "Esc" key.
You can disable it from the Editing tab of Special:Preferences by checking the "Do not show link suggest in Source mode" option.