By default, the <Alt> and <Option> keys are the same as <Meta>. The Mac <Cmd> key is the same as <Super>, and Emacs provides a set of key bindings using this modifier key that mimic other Mac / GNUstep applications (see Mac / GNUstep Events). You can change these bindings in the usual way (see Key Bindings).
ns-right-alternate-modifier controls the
behavior of the right <Alt> and <Option> keys. These keys
behave like the left-hand keys if the value is
default). A value of
hyper makes them behave like the corresponding
modifier keys; a value of
left means be the same key as
ns-alternate-modifier; a value of
none tells Emacs to
ignore them, in which case you get the default behavior of macOS
accentuation system from the right <Option> key.
S-mouse-1 adjusts the region to the click position,
just like mouse-3 (
mouse-save-then-kill); it does not pop
up a menu for changing the default face, as S-mouse-1 normally
does (see Text Scale). This change makes Emacs behave more like
other Mac / GNUstep applications.
When you open or save files using the menus, or using the Cmd-o and Cmd-S bindings, Emacs uses graphical file dialogs to read file names. However, if you use the regular Emacs key sequences, such as C-x C-f, Emacs uses the minibuffer to read file names.
On GNUstep, in an X-windows environment you need to use Cmd-c instead of one of the C-w or M-w commands to transfer text to the X primary selection; otherwise, Emacs will use the clipboard selection. Likewise, Cmd-y (instead of C-y) yanks from the X primary selection instead of the kill-ring or clipboard.
Many programs which may run under Emacs, like latex or man, depend on the settings of environment variables. If Emacs is launched from the shell, it will automatically inherit these environment variables and its subprocesses will inherit them from it. But if Emacs is launched from the Finder it is not a descendant of any shell, so its environment variables haven't been set, which often causes the subprocesses it launches to behave differently than they would when launched from the shell.
For the PATH and MANPATH variables, a system-wide method of setting PATH is recommended on macOS, using the /etc/paths files and the /etc/paths.d directory.