Function: minibuffer-electric-default-mode

Toggle Minibuffer Electric Default mode.
With a prefix argument ARG, enable Minibuffer Electric Default
mode if ARG is positive, and disable it otherwise. If called
from Lisp, enable the mode if ARG is omitted or nil.

Minibuffer Electric Default mode is a global minor mode. When
enabled, minibuffer prompts that show a default value only show
the default when it's applicable -- that is, when hitting RET
would yield the default value. If the user modifies the input
such that hitting RET would enter a non-default value, the prompt
is modified to remove the default indication. (fn &optional ARG)

Variable: minibuffer-electric-default-mode

Non-nil if Minibuffer-Electric-Default mode is enabled.
See the command `minibuffer-electric-default-mode' for a description of this minor mode.
Setting this variable directly does not take effect;
either customize it (see the info node `Easy Customization')
or call the function `minibuffer-electric-default-mode'.