GNU Emacs Manual - Expanding Abbrevs

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## Controlling Abbrev Expansion

An abbrev expands whenever it is present in the buffer just before point and you type a self-inserting whitespace or punctuation character (`SPC`, comma, etc.). More precisely, any character that is not a word constituent expands an abbrev, and any word-constituent character can be part of an abbrev. The most common way to use an abbrev is to insert it and then insert a punctuation character to expand it.

Abbrev expansion preserves case; thus, ``foo'` expands into ``find outer otter'`; ``Foo'` into ``Find outer otter'`, and ``FOO'` into ``FIND OUTER OTTER'` or ``Find Outer Otter'` according to the variable `abbrev-all-caps` (a non-`nil` value chooses the first of the two expansions).

These commands are used to control abbrev expansion:

`M-'`
  Separate a prefix from a following abbrev to be expanded (`abbrev-prefix-mark`).
`C-x a e`
  Expand the abbrev before point (`expand-abbrev`). This is effective even when Abbrev mode is not enabled.
`M-x expand-region-abbrevs`
  Expand some or all abbrevs found in the region.

You may wish to expand an abbrev with a prefix attached; for example, if ``cnst'` expands into ``construction'`, you might want to use it to enter ``reconstruction'`. It does not work to type `recnst`, because that is not necessarily a defined abbrev. What you can do is use the command `M-'` (`abbrev-prefix-mark`) in between the prefix ``re'` and the abbrev ``cnst'`. First, insert ``re'`. Then type `M-'`; this inserts a hyphen in the buffer to indicate that it has done its work. Then insert the abbrev ``cnst'`; the buffer now contains ``re-cnst'`. Now insert a non-word character to expand the abbrev ``cnst'` into ``construction'`. This expansion step also deletes the hyphen that indicated `M-'` had been used. The result is the desired ``reconstruction'`.

If you actually want the text of the abbrev in the buffer, rather than its expansion, you can accomplish this by inserting the following punctuation with `C-q`. Thus, `foo C-q ,` leaves ``foo,'` in the buffer.

If you expand an abbrev by mistake, you can undo the expansion and bring back the abbrev itself by typing `C-_` to undo (see section Undoing Changes). This also undoes the insertion of the non-word character that expanded the abbrev. If the result you want is the terminating non-word character plus the unexpanded abbrev, you must reinsert the terminating character, quoting it with `C-q`. You can also use the command `M-x unexpand-abbrev` to cancel the last expansion without deleting the terminating character.

`M-x expand-region-abbrevs` searches through the region for defined abbrevs, and for each one found offers to replace it with its expansion. This command is useful if you have typed in text using abbrevs but forgot to turn on Abbrev mode first. It may also be useful together with a special set of abbrev definitions for making several global replacements at once. This command is effective even if Abbrev mode is not enabled.

Expanding an abbrev runs the hook `pre-abbrev-expand-hook` (see section Hooks).

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