read-regexp-defaults-function

read-regexp-defaults-function is a variable defined in `replace.el'.
Its value is

nil

• This variable may be risky if used as a file-local variable.

Documentation:
Function that provides default regexp(s) for `read-regexp'.
This function should take no arguments and return one of: nil, a
regexp, or a list of regexps. Interactively, `read-regexp' uses
the return value of this function for its DEFAULT argument.

As an example, set this variable to `find-tag-default-as-regexp'
to default to the symbol at point.

To provide different default regexps for different commands,
the function that you set this to can check `this-command'.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.4 of Emacs.