Autoformat is an optional feature that your platform may (or may not) have enabled. If you are a developer, you can enable it by parameters.

Autoformat replaces some symbols from keyboard by their better looking counterparts. At present the replacements are:

The replacement is done while you type, so you never see the actual key pressed.

Autoformat also auto-closes parentheses and alike. When you type the left fence, the right fence is automatically inserted.

These are the enclosers that have this feature:

If you want to modify this automatic end symbol, place the cursor to the left of the symbol and write the alternate end symbol. This only works with the end symbol. If you want to replace the automatic open symbol, you must insert a new left/right pair.

See this example of an open-closed interval: