emacs: Modifier Keys
51.3.7 Modifier Keys
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The default key bindings in Emacs are set up so that modified
alphabetical characters are case-insensitive. In other words, ‘C-A’
does the same thing as ‘C-a’, and ‘M-A’ does the same thing as ‘M-a’.
This concerns only alphabetical characters, and does not apply to
shifted versions of other keys; for instance, ‘C-@’ is not the same as
‘C-2’.
A <Control>-modified alphabetical character is always considered
case-insensitive: Emacs always treats ‘C-A’ as ‘C-a’, ‘C-B’ as ‘C-b’,
and so forth. The reason for this is historical.
For all other modifiers, you can make the modified alphabetical
characters case-sensitive when you customize Emacs. For instance, you
could make ‘M-a’ and ‘M-A’ run different commands.
Although only the <Control> and <META> modifier keys are commonly
used, Emacs supports three other modifier keys. These are called
<Super>, <Hyper> and <Alt>. Few terminals provide ways to use these
modifiers; the key labeled <Alt> on most keyboards usually issues the
<META> modifier, not <Alt>. The standard key bindings in Emacs do not
include any characters with these modifiers. However, you can customize
Emacs to assign meanings to them. The modifier bits are labeled as
‘s-’, ‘H-’ and ‘A-’ respectively.
Even if your keyboard lacks these additional modifier keys, you can
enter it using ‘C-x @’: ‘C-x @ h’ adds the Hyper flag to the next
character, ‘C-x @ s’ adds the Super flag, and ‘C-x @ a’ adds the Alt
flag. For instance, ‘C-x @ h C-a’ is a way to enter ‘Hyper-Control-a’.
(Unfortunately, there is no way to add two modifiers by using ‘C-x @’
twice for the same character, because the first one goes to work on the
‘C-x’.)
Info Catalog
emacs: Init Rebinding
emacs: Key Bindings
emacs: Function Keys