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15.1.4 Special Input for Incremental Search

Some of the characters you type during incremental search have special effects.

By default, incremental search performs lax space matching: each space, or sequence of spaces, matches any sequence of one or more spaces in the text. Hence, ‘foo bar’ matches ‘foo bar’, ‘foo bar’, ‘foo bar’, and so on (but not ‘foobar’). More precisely, Emacs matches each sequence of space characters in the search string to a regular expression specified by the variable search-whitespace-regexp. For example, to make spaces match sequences of newlines as well as spaces, set it to ‘"[[:space:]\n]+"’.

To toggle lax space matching, type M-s SPC (isearch-toggle-lax-whitespace). To disable this feature entirely, change search-whitespace-regexp to nil; then each space in the search string matches exactly one space.

If the search string you entered contains only lower-case letters, the search is case-insensitive; as long as an upper-case letter exists in the search string, the search becomes case-sensitive. If you delete the upper-case character from the search string, it ceases to have this effect. See Search Case.

To toggle whether or not invisible text is searched, type M-s i (isearch-toggle-invisible). See Outline Search.

To search for a newline character, type C-j.

To search for non-ASCII characters, use one of the following methods:

Typing M-% in incremental search invokes query-replace or query-replace-regexp (depending on search mode) with the current search string used as the string to replace. A negative prefix argument means to replace backward. See Query Replace.

Typing M-TAB in incremental search invokes isearch-complete, which attempts to complete the search string using the search ring as a list of completion alternatives. See Completion. In many operating systems, the M-TAB key sequence is captured by the window manager; you then need to rebind isearch-complete to another key sequence if you want to use it (see Rebinding).

When incremental search is active, you can type C-h C-h to access interactive help options, including a list of special key bindings. These key bindings are part of the keymap isearch-mode-map (see Keymaps).

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