This is an experimental feature that can be extremely helpful, especially for editing Regular Expression patterns inside String literals due to the double escaping requirement. For example, in a regular expression, a literal backslash character has to be written as a double backslash and each of them has to be escaped with another backslash when written inside a String literal.
The Quick Edit function that appears as an Intention Action for any injected language fragment displays a pop-up dialog that allows you to edit the string's value without the double escaping requirement. The dialog also shows the particular prefix/suffix of the fragment in a non-editable area.
The pop-up window can be dismissed by pressing Escape or clicking somewhere outside the pop-up window. Any changes made in the pop-up window are committed by pressing Ctrl-Enter.
Please note that the formatting of the non-editable prefix/suffix may differ from the actual value due to some problems. However, even though the formatting/alignment of the editable text may differ from the expected text, making changes to the text still works as expected.