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355 lines
14 KiB
EmacsLisp
355 lines
14 KiB
EmacsLisp
;;; help-at-pt.el --- local help through the keyboard
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;; Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
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;; Author: Luc Teirlinck <teirllm@auburn.edu>
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;; Keywords: help
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;; This file is part of GNU Emacs.
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;; GNU Emacs is free software: you can redistribute it and/or modify
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;; it under the terms of the GNU General Public License as published by
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;; the Free Software Foundation, either version 3 of the License, or
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;; (at your option) any later version.
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;; GNU Emacs is distributed in the hope that it will be useful,
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;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;; GNU General Public License for more details.
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;; You should have received a copy of the GNU General Public License
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;; along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>.
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;;; Commentary:
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;; This file contains functionality to make the help provided by the
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;; help-echo text or overlay property available to the keyboard user.
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;; It also supports a more keyboard oriented alternative to
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;; `help-echo', namely a new text or overlay property `kbd-help'.
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;;
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;; It provides facilities to access the local help available at point
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;; either on demand, using the command `display-local-help', or
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;; automatically after a suitable idle time, through the customizable
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;; variable `help-at-pt-display-when-idle'.
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;;
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;; You can get a more global overview of the local help available in
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;; the buffer, using the commands `scan-buf-next-region' and
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;; `scan-buf-previous-region', which move to the start of the next or
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;; previous region with available local help and print the help found
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;; there.
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;;
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;; Suggested key bindings:
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;;
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;; (global-set-key [C-tab] 'scan-buf-next-region)
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;; (global-set-key [C-M-tab] 'scan-buf-previous-region)
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;;
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;; You do not have to do anything special to use the functionality
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;; provided by this file, because all important functions autoload.
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;;; Code:
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(defgroup help-at-pt nil
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"Features for displaying local help."
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:group 'help
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:version "22.1")
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;;;###autoload
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(defun help-at-pt-string (&optional kbd)
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"Return the help-echo string at point.
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Normally, the string produced by the `help-echo' text or overlay
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property, or nil, is returned.
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If KBD is non-nil, `kbd-help' is used instead, and any
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`help-echo' property is ignored. In this case, the return value
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can also be t, if that is the value of the `kbd-help' property."
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(let* ((prop (if kbd 'kbd-help 'help-echo))
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(pair (get-char-property-and-overlay (point) prop))
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(val (car pair))
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(ov (cdr pair)))
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(if (functionp val)
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(funcall val (selected-window) (if ov ov (current-buffer)) (point))
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(eval val))))
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;;;###autoload
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(defun help-at-pt-kbd-string ()
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"Return the keyboard help string at point.
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If the `kbd-help' text or overlay property at point produces a
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string, return it. Otherwise, use the `help-echo' property. If
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this produces no string either, return nil."
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(let ((kbd (help-at-pt-string t))
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(echo (help-at-pt-string)))
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(if (and kbd (not (eq kbd t))) kbd echo)))
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;;;###autoload
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(defun display-local-help (&optional arg)
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"Display local help in the echo area.
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This displays a short help message, namely the string produced by
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the `kbd-help' property at point. If `kbd-help' does not produce
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a string, but the `help-echo' property does, then that string is
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printed instead.
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A numeric argument ARG prevents display of a message in case
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there is no help. While ARG can be used interactively, it is
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mainly meant for use from Lisp."
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(interactive "P")
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(let ((help (help-at-pt-kbd-string)))
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(if help
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(message "%s" help)
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(if (not arg) (message "No local help at point")))))
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(defvar help-at-pt-timer nil
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"Non-nil means that a timer is set that checks for local help.
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If non-nil, this is the value returned by the call of
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`run-with-idle-timer' that set that timer. This variable is used
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internally to enable `help-at-pt-display-when-idle'. Do not set it
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yourself.")
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(defcustom help-at-pt-timer-delay 1
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"Delay before displaying local help.
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This is used if `help-at-pt-display-when-idle' is enabled.
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The value may be an integer or floating point number.
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If a timer is already active, there are two ways to make the new
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value take effect immediately. After setting the value, you can
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first call `help-at-pt-cancel-timer' and then set a new timer
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with `help-at-pt-set-timer'. Alternatively, you can set this
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variable through Custom. This will not set a timer if none is
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active, but if one is already active, Custom will make it use the
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new value."
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:group 'help-at-pt
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:type 'number
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:initialize 'custom-initialize-default
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:set (lambda (variable value)
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(set-default variable value)
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(and (boundp 'help-at-pt-timer)
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help-at-pt-timer
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(timer-set-idle-time help-at-pt-timer value t))))
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;;;###autoload
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(defun help-at-pt-cancel-timer ()
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"Cancel any timer set by `help-at-pt-set-timer'.
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This disables `help-at-pt-display-when-idle'."
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(interactive)
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(let ((inhibit-quit t))
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(when help-at-pt-timer
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(cancel-timer help-at-pt-timer)
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(setq help-at-pt-timer nil))))
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;;;###autoload
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(defun help-at-pt-set-timer ()
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"Enable `help-at-pt-display-when-idle'.
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This is done by setting a timer, if none is currently active."
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(interactive)
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(unless help-at-pt-timer
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(setq help-at-pt-timer
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(run-with-idle-timer
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help-at-pt-timer-delay t #'help-at-pt-maybe-display))))
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;;;###autoload
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(defcustom help-at-pt-display-when-idle 'never
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"Automatically show local help on point-over.
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If the value is t, the string obtained from any `kbd-help' or
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`help-echo' property at point is automatically printed in the
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echo area, if nothing else is already displayed there, or after a
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quit. If both `kbd-help' and `help-echo' produce help strings,
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`kbd-help' is used. If the value is a list, the help only gets
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printed if there is a text or overlay property at point that is
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included in this list. Suggested properties are `keymap',
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`local-map', `button' and `kbd-help'. Any value other than t or
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a non-empty list disables the feature.
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This variable only takes effect after a call to
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`help-at-pt-set-timer'. The help gets printed after Emacs has
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been idle for `help-at-pt-timer-delay' seconds. You can call
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`help-at-pt-cancel-timer' to cancel the timer set by, and the
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effect of, `help-at-pt-set-timer'.
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When this variable is set through Custom, `help-at-pt-set-timer'
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is called automatically, unless the value is `never', in which
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case `help-at-pt-cancel-timer' is called. Specifying an empty
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list of properties through Custom will set the timer, thus
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enabling buffer local values. It sets the actual value to nil.
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Thus, Custom distinguishes between a nil value and other values
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that disable the feature, which Custom identifies with `never'.
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The default is `never'."
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:group 'help-at-pt
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:type '(choice (const :tag "Always"
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:format "%t\n%h"
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:doc
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"This choice can get noisy.
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The text printed from the `help-echo' property is often only
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relevant when using the mouse. If you mind about too many
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messages getting printed in the echo area, use \"In certain
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situations\". See the documentation there for more information."
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t)
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(repeat :tag "In certain situations"
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;; unless we specify 0 offset the doc string
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;; for this choice gets indented very
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;; differently than for the other two
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;; choices, when "More" is selected.
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:offset 0
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:format "%{%t%}:\n%v%i\n%h"
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:doc
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"This choice lets you specify a list of \
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text properties.
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Presence of any of these properties will trigger display of
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available local help on point-over.
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If you use this alternative through Custom without listing any
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properties, a timer will be set anyway. This will enable buffer
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local values. Use \"Never\" if you do not want a timer to be set.
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Suggested properties:
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The `keymap' and `local-map' properties change keybindings in
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parts of the buffer. Some of these keymaps are mode independent
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and are not mentioned in the mode documentation. Hence, the help
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text is likely to be useful.
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Specifying `button' is relevant in Custom and similar buffers.
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In these buffers, most, but not all, of the text shown this way is
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available by default when using tab, but not on regular point-over.
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The presence of a `kbd-help' property guarantees that non mouse
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specific help is available."
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:value (keymap local-map button kbd-help)
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symbol)
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(other :tag "Never"
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:format "%t\n%h"
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:doc
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"This choice normally disables buffer local values.
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If you choose this value through Custom and a timer checking for
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local help is currently active, it will be canceled. No new
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timer will be set. Call `help-at-pt-set-timer' after choosing
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this option, or use \"In certain situations\" and specify no text
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properties, to enable buffer local values."
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never))
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:initialize 'custom-initialize-default
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:set #'(lambda (variable value)
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(set-default variable value)
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(if (eq value 'never)
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(help-at-pt-cancel-timer)
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(help-at-pt-set-timer)))
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:set-after '(help-at-pt-timer-delay)
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:require 'help-at-pt)
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;; Function for use in `help-at-pt-set-timer'.
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(defun help-at-pt-maybe-display ()
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(and (or (eq help-at-pt-display-when-idle t)
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(and (consp help-at-pt-display-when-idle)
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(catch 'found
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(dolist (prop help-at-pt-display-when-idle)
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(if (get-char-property (point) prop)
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(throw 'found t))))))
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(or (not (current-message))
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(string= (current-message) "Quit"))
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(display-local-help t)))
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;;;###autoload
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(defun scan-buf-move-to-region (prop &optional arg hook)
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"Go to the start of the next region with non-nil PROP property.
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Then run HOOK, which should be a quoted symbol that is a normal
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hook variable, or an expression evaluating to such a symbol.
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Adjacent areas with different non-nil PROP properties are
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considered different regions.
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With numeric argument ARG, move to the start of the ARGth next
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such region, then run HOOK. If ARG is negative, move backward.
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If point is already in a region, then that region does not count
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toward ARG. If ARG is 0 and point is inside a region, move to
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the start of that region. If ARG is 0 and point is not in a
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region, print a message to that effect, but do not move point and
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do not run HOOK. If there are not enough regions to move over,
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an error results and the number of available regions is mentioned
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in the error message. Point is not moved and HOOK is not run."
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(cond ((> arg 0)
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(if (= (point) (point-max))
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(error "No further `%s' regions" prop))
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(let ((pos (point)))
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(dotimes (x arg)
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(setq pos (next-single-char-property-change pos prop))
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(unless (get-char-property pos prop)
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(setq pos (next-single-char-property-change pos prop))
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(unless (get-char-property pos prop)
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(cond ((= x 0)
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(error "No further `%s' regions" prop))
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((= x 1)
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(error "There is only one further `%s' region" prop))
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(t
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(error
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"There are only %d further `%s' regions"
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x prop))))))
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(goto-char pos)
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(run-hooks hook)))
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((= arg 0)
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(let ((val (get-char-property (point) prop)))
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(cond ((not val)
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(message "Point is not in a `%s' region" prop))
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((eq val (get-char-property (1- (point)) prop))
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(goto-char
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(previous-single-char-property-change (point) prop))
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(run-hooks hook))
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(t (run-hooks hook)))))
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((< arg 0)
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(let ((pos (point)) (val (get-char-property (point) prop)))
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(and val
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(eq val (get-char-property (1- pos) prop))
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(setq pos
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(previous-single-char-property-change pos prop)))
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(if (= pos (point-min))
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(error "No prior `%s' regions" prop))
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(dotimes (x (- arg))
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(setq pos (previous-single-char-property-change pos prop))
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(unless (get-char-property pos prop)
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(setq pos (previous-single-char-property-change pos prop))
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(unless (get-char-property pos prop)
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(cond ((= x 0)
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(error "No prior `%s' regions" prop))
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((= x 1)
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(error "There is only one prior `%s' region" prop))
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(t
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(error "There are only %d prior `%s' regions"
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x prop))))))
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(goto-char pos)
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(run-hooks hook)))))
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;; To be moved to a different file and replaced by a defcustom in a
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;; future version.
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(defvar scan-buf-move-hook '(display-local-help)
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"Normal hook run by `scan-buf-next-region'.
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Also used by `scan-buf-previous-region'. The hook is run after
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positioning point.")
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;;;###autoload
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(defun scan-buf-next-region (&optional arg)
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"Go to the start of the next region with non-nil help-echo.
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Print the help found there using `display-local-help'. Adjacent
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areas with different non-nil help-echo properties are considered
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different regions.
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With numeric argument ARG, move to the start of the ARGth next
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help-echo region. If ARG is negative, move backward. If point
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is already in a help-echo region, then that region does not count
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toward ARG. If ARG is 0 and point is inside a help-echo region,
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move to the start of that region. If ARG is 0 and point is not
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in such a region, just print a message to that effect. If there
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are not enough regions to move over, an error results and the
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number of available regions is mentioned in the error message.
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A potentially confusing subtlety is that point can be in a
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help-echo region without any local help being available. This is
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because `help-echo' can be a function evaluating to nil. This
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rarely happens in practice."
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(interactive "p")
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(scan-buf-move-to-region 'help-echo arg 'scan-buf-move-hook))
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;;;###autoload
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(defun scan-buf-previous-region (&optional arg)
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"Go to the start of the previous region with non-nil help-echo.
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Print the help found there using `display-local-help'. Adjacent
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areas with different non-nil help-echo properties are considered
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different regions. With numeric argument ARG, behaves like
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`scan-buf-next-region' with argument -ARG.."
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(interactive "p")
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(scan-buf-move-to-region 'help-echo (- arg) 'scan-buf-move-hook))
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(provide 'help-at-pt)
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;; arch-tag: d0b8b86d-d23f-45d0-a82d-208d6205a583
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;;; help-at-pt.el ends here
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