pop-up-frame-alist

pop-up-frame-alist is a variable defined in `window.el'.
Its value is

nil

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

Documentation:
Alist of parameters for automatically generated new frames.
If non-nil, the value you specify here is used by the default
`pop-up-frame-function' for the creation of new frames.

Since `pop-up-frame-function' is used by `display-buffer' for
making new frames, any value specified here by default affects
the automatic generation of new frames via `display-buffer' and
all functions based on it. The behavior of `make-frame' is not
affected by this variable.

You can customize this variable.