Escape leaves search mode and returns to the point where search
was started, while Enter or Return stay at the current position and
additionally stores the first match in the current line into the primary
-selection.
+selection if the Shift modifier is active.
The regex defaults to "(?i)", resulting in a case-insensitive search. To
get a case-sensitive search you can delete this prefix using BackSpace
or simply use an uppercase character which removes the "(?i)" prefix.