An abbrev is a word that has been defined to expand into a
specified expansion. When you insert a word-separator character
following the abbrev, that expands the abbrev—replacing the
abbrev with its expansion. For example, if ‘foo’ is defined as
an abbrev expanding to ‘find outer otter’, then typing f o o .
will insert ‘find outer otter.’. Abbrevs expand only when Abbrev
mode, a buffer-local minor mode, is enabled. Disabling Abbrev
mode does not cause abbrev definitions to be forgotten, but they
do not expand until Abbrev mode is enabled again. The command
M-x abbrev-mode toggles Abbrev mode; with a numeric argument, it
turns Abbrev mode on if the argument is positive, off otherwise.
See Minor Modes. Abbrevs can have mode-specific definitions,
active only in one major mode. Abbrevs can also have global
definitions that are active in all major modes. The same abbrev
can have a global definition and various mode-specific
definitions for different major modes. A mode-specific
definition for the current major mod