|[ < ]||[ > ]||[ << ]||[ Up ]||[ >> ]||[Top]||[Contents]||[Index]||[ ? ]|
There are three different ways that RET can work in completing minibuffers, depending on how the argument will be used.
Cautious completion is used for reading file names for files that must already exist.
The completion commands display a list of all possible completions in a window whenever there is more than one possibility for the very next character. Also, typing ? explicitly requests such a list. If the list of completions is long, you can scroll it with C-M-v (see section O.3 Using Other Windows).