same-window-regexps

same-window-regexps is a variable defined in `window.el'.
Its value is

nil

Documentation:
List of regexps saying which buffers should appear in the "same" window.
`display-buffer' and `pop-to-buffer' show a buffer whose name
matches a regexp on this list in the selected rather than some
other window.

An element of this list can be a cons cell instead of just a
string. In that case, the cell's car must be a regexp matching
the buffer name. This is for compatibility with
`special-display-regexps'; the cdr of the cons cell is ignored.

See also `same-window-buffer-names'.

You can customize this variable.