Return number of lines by which WINDOW can be shrunk.
WINDOW must be a valid window and defaults to the selected one.
Return zero if WINDOW cannot be shrunk.
Optional argument HORIZONTAL non-nil means return number of
columns by which WINDOW can be shrunk.
Optional argument IGNORE non-nil means ignore restrictions
imposed by fixed size windows, `window-min-height' or
`window-min-width' settings. If IGNORE is a window, ignore
restrictions for that window only. If IGNORE equals `safe',
live windows may get as small as `window-safe-min-height' lines
and `window-safe-min-width' columns. Any other non-nil value
means ignore all of the above restrictions for all windows.
Optional argument TRAIL restricts the windows that can be enlarged.
If its value is `before', only windows to the left of or above WINDOW
can be enlarged. If it is `after', only windows to the right of or
below WINDOW can be enlarged.
Optional argument NOUP non-nil means don't go up in the window
tree, but try to enlarge windows within WINDOW's combination only.
Optional argument NODOWN non-nil means don't check whether WINDOW
itself (and its child windows) can be shrunk; check only whether
at least one other window can be enlarged appropriately.