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28.3.4 Implied Frame Resizing

By default, Emacs tries to keep the number of lines and columns of a frame's text area unaltered when, for example, adding or removing the menu bar, changing the default font or setting the width of the frame's scroll bars. This means, however, that in such case Emacs must ask the window manager to resize the outer frame in order to accommodate the size change. Note that wrapping a menu or tool bar usually does not resize the frame's outer size, hence this will alter the number of displayed lines.

Occasionally, such implied frame resizing may be unwanted, for example, when the frame is maximized or made full-screen (where it's turned off by default). In other cases you can disable implied resizing with the following option:

— User Option: frame-inhibit-implied-resize

If this option is nil, changing font, menu bar, tool bar, internal borders, fringes or scroll bars of a specific frame may implicitly resize the frame's display area in order to preserve the number of columns or lines the frame displays. If this option is non-nil, no implied resizing is done.

The value of this option can be also be a list of frame parameters. In that case, implied resizing is inhibited when changing a parameter that appears in this list. The frame parameters currently handled by this option are: font, font-backend, internal-border-width, menu-bar-lines and tool-bar-lines.

Changing any of the scroll-bar-width, scroll-bar-height, vertical-scroll-bars, horizontal-scroll-bars, left-fringe and right-fringe frame parameters is handled as if the frame contained just one live window. This means, for example, that removing vertical scroll bars on a frame containing several side by side windows will shrink the outer frame width by the width of one scroll bar provided this option is nil and keep it unchanged if this option is either t or a list containing vertical-scroll-bars.

The default value is '(tool-bar-lines) for Lucid, Motif and Windows (which means that adding/removing a tool bar there does not change the outer frame height), nil on all other window systems including GTK+ (which means that changing any of the parameters listed above may change the size of the outer frame), and t otherwise (which means the outer frame size never changes implicitly when there's no window system support).

Note that when a frame is not large enough to accommodate a change of any of the parameters listed above, Emacs may try to enlarge the frame even if this option is non-nil.