documentation/api.md

   1 <!--
   2 This is part of the VimFx documentation.
   3 Copyright Simon Lydell 2015, 2016.
   4 See the file README.md for copying conditions.
   5 -->
   6
   7 # API
   8
   9 This file documents VimFx’s [config file] API.
  10
  11 Both `config.js` and `frame.js` have access to a variable called `vimfx`. Note
  12 that while the variables have the same name, they are different and provide
  13 different API methods.
  14
  15
  16 ## `config.js` API
  17
  18 In `config.js`, the following API is available as the variable `vimfx`.
  19
  20 ### `vimfx.get(...)`, `vimfx.getDefault(...)` and `vimfx.set(...)`
  21
  22 Gets or sets the (default) value of a VimFx pref.
  23
  24 You can see all prefs in [defaults.coffee], or by opening [about:config] and
  25 filtering by `extensions.vimfx`. Note that you can also access the [special
  26 options], which may not be accessed in [about:config], using `vimfx.get(...)`
  27 and `vimfx.set(...)`—in fact, this is the _only_ way of accessing those options.
  28
  29 #### `vimfx.get(pref)`
  30
  31 Gets the value of the VimFx pref `pref`.
  32
  33 ```js
  34 // Get the value of the Hint chars option:
  35 vimfx.get('hint_chars')
  36 // Get all keyboard shortcuts (as a string) for the `f` command:
  37 vimfx.get('mode.normal.follow')
  38 ```
  39
  40 #### `vimfx.getDefault(pref)`
  41
  42 Gets the default value of the VimFx pref `pref`.
  43
  44 Useful when you wish to extend a default, rather than replacing it. See below.
  45
  46 #### `vimfx.set(pref, value)`
  47
  48 Sets the value of the VimFx pref `pref` to `value`.
  49
  50 ```js
  51 // Set the value of the Hint chars option:
  52 vimfx.set('hint_chars', 'abcdefghijklmnopqrstuvwxyz')
  53 // Add yet a keyboard shortcut for the `f` command:
  54 vimfx.set('mode.normal.follow', vimfx.getDefault('mode.normal.follow') + '  e')
  55 ```
  56
  57 When extending a pref (as in the second example above), be sure to use
  58 `vimfx.getDefault` rather than `vimfx.get`. Otherwise you get a multiplying
  59 effect. In the above example, after starting Firefox a few times the pref would
  60 be `f  e  e  e  e`. Also, if you find that example very verbose: Remember that
  61 you’re using a programming language! Write a small helper function that suits
  62 your needs.
  63
  64 Note: If you produce conflicting keyboard shortcuts, the order of your code does
  65 not matter. The command that comes first in VimFx’s settings page in the Add-ons
  66 Manager (and in the Keyboard Shortcuts help dialog) gets the shortcut; the other
  67 one(s) do(es) not. See the notes about order in [mode object], [category object]
  68 and [command object] for more information about order.
  69
  70 ```js
  71 // Even though we set the shortcut for focusing the search bar last, the command
  72 // for focusing the location bar “wins”, because it comes first in VimFx’s
  73 // settings page in the Add-ons Manager.
  74 vimfx.set('mode.normal.focus_location_bar', 'ö')
  75 vimfx.set('mode.normal.focus_search_bar', 'ö')
  76
  77 // Swapping their orders also swaps the “winner”.
  78 let {commands} = vimfx.modes.normal
  79 ;[commands.focus_location_bar.order, commands.focus_search_bar.order] =
  80   [commands.focus_search_bar.order, commands.focus_location_bar.order]
  81 ```
  82
  83 ### `vimfx.addCommand(options, fn)`
  84
  85 Creates a new command.
  86
  87 `options`:
  88
  89 - name: `String`. The name used when accessing the command via
  90   `vimfx.modes[options.mode].commands[options.name]`. It is also used for the
  91   pref used to store the shortcuts for the command:
  92   `` `custom.mode.${options.mode}.${options.name}` ``.
  93 - description: `String`. Shown in the Keyboard Shortcuts help dialog and VimFx’s
  94   settings page in the Add-ons Manager.
  95 - mode: `String`. Defaults to `'normal'`. The mode to add the command to. The
  96   value has to be one of the keys of [`vimfx.modes`].
  97 - category: `String`. Defaults to `'misc'` for Normal mode and `''`
  98   (uncategorized) otherwise. The category to add the command to. The
  99   value has to be one of the keys of [`vimfx.get('categories')`][categories].
 100 - order: `Number`. Defaults to putting the command at the end of the category.
 101   The first of the default commands has the order `100` and then they increase
 102   by `100` per command. This allows to put new commands between two already
 103   existing ones.
 104
 105 `fn` is called when the command is activated. See the [onInput] documentation
 106 below for more information.
 107
 108 <strong id="custom-command-shortcuts">Note</strong> that you have to give the
 109 new command a shortcut in VimFx’s settings page in the Add-ons Manager or set
 110 one using `vimfx.set(...)` to able to use the new command.
 111
 112 ```js
 113 vimfx.addCommand({
 114   name: 'hello',
 115   description: 'Log Hello World',
 116 }, => {
 117   console.log('Hello World!')
 118 })
 119 // Optional:
 120 vimfx.set('custom.mode.normal.hello', 'gö')
 121 ```
 122
 123 ### `vimfx.addOptionOverrides(...)` and `vimfx.addKeyOverrides(...)`
 124
 125 These methods take any number of arguments. Each argument is a rule. The rules
 126 are added in order. The methods may be run multiple times.
 127
 128 A rule is an `Array` of length 2:
 129
 130 1. The first item is a function that returns `true` if the rule should be
 131    applied and `false` if not. This is called the matching function.
 132 2. The second item is the value that should be used if the rule is applied. This
 133    is called the override.
 134
 135 The rules are tried in the same order they were added. When a matching rule is
 136 found it is applied. No more rules will be applied.
 137
 138 #### `vimfx.addOptionOverrides(...rules)`
 139
 140 The rules are matched any time the value of a VimFx pref is needed.
 141
 142 The matching function receives a [location object].
 143
 144 The override is an object whose keys are VimFx pref names and whose values
 145 override the pref in question. The values should be formatted as in an [options
 146 object].
 147
 148 ```js
 149 vimfx.addOptionOverrides(
 150   [ ({hostname, pathname, hash}) =>
 151     `${hostname}${pathname}${hash}` === 'google.com/',
 152     {prevent_autofocus: false}
 153   ]
 154 )
 155 ```
 156
 157 #### `vimfx.addKeyOverrides(...rules)`
 158
 159 The rules are matched any time you press a key that is not part of the tail of a
 160 multi-key shortcut.
 161
 162 The matching function receives a [location object] as well as the current
 163 mode name (one of the keys of [`vimfx.modes`]).
 164
 165 The override is an array of keys which should not activate VimFx commands but be
 166 sent to the page.
 167
 168 This allows to disable commands on specific sites. To _add_ commands on specific
 169 sites, add them globally and then disable them on all _other_ sites.
 170
 171 ```js
 172 vimfx.addKeyOverrides(
 173   [ location => location.hostname === 'facebook.com',
 174     ['j', 'k']
 175   ]
 176 )
 177 ```
 178
 179 ### `vimfx.send(vim, message, data = null, callback = null)`
 180
 181 Send `message` (a string) to the instance of `frame.js` in the tab managed by
 182 [`vim`][vim object], and pass it `data`. If provided, `callback` must be a
 183 function that takes a single argument, which is the data that `frame.js`
 184 responds with. `frame.js` uses its [`vimfx.listen(...)`] method to listen for
 185 (and optionally respond to) `message`.
 186
 187 Here is an example:
 188
 189 ```js
 190 // config.js
 191 // You get a `vim` instance by using `vimfx.addCommand(...)` or `vimfx.on(...)`.
 192 vimfx.send(vim, 'getSelection', {example: 5}, selection => {
 193   console.log('Currently selected text:', selection)
 194 })
 195 ```
 196
 197 ```js
 198 // frame.js
 199 vimfx.listen('getSelection', ({example}, callback) => {
 200   console.log('`example` should be 5:', example)
 201   let selection = content.getSelection().toString()
 202   callback(selection)
 203 })
 204 ```
 205
 206 What if you want to do it the other way around: Send a message _from_ `frame.js`
 207 and listen for it in `config.js`? That’s not the common use case, so VimFx does
 208 not provide convenience functions for it. Yes, `vimfx.send(...)`, and
 209 `vimfx.listen(...)` in `frame.js`, are just light wrappers around the standard
 210 Firefox [Message Manager] to make it easier to create custom commands that ask
 211 `frame.js` for information about the current web page (as in the above example).
 212 If you want to send messages any other way, you’ll need to use the Message
 213 Manager directly. See [the `shutdown` event] for an example.
 214
 215 (While it would have made sense to provide `vim.send(message, data, callback)`
 216 instead of `vimfx.send(vim, message, data, callback)`, the latter was chosen for
 217 symmetry between `config.js` and `frame.js`. Use `vimfx.send()` to send
 218 messages, and `vimfx.listen()` to listen for them.)
 219
 220 ### `vimfx.on(eventName, listener)` and `vimfx.off(eventName, listener)`
 221
 222 After calling `vimfx.on(eventName, listener)`, `listener(data)` will be called
 223 when `eventName` is fired.
 224
 225 You may use `vimfx.off(eventName, listener)` if you’d like to remove your
 226 added listener for some reason.
 227
 228 While [`vimfx.send(...)`] and [`vimfx.listen(...)`] are all about passing
 229 messages between `config.js` and `frame.js`, `vimfx.on(...)` is all about doing
 230 something whenever VimFx emits internal events.
 231
 232 #### The `locationChange` event
 233
 234 Occurs when opening a new tab, navigating to a new URL or refreshing the page,
 235 causing a full page load. The data passed to listeners is an object with the
 236 following properties:
 237
 238 - vim: The current [vim object].
 239 - location: A [location object].
 240
 241 This can be used to enter a different mode by default on some pages (which can
 242 be used to replace the blacklist option).
 243
 244 ```js
 245 vimfx.on('locationChange', ({vim, location}) => {
 246   if (location.hostname === 'example.com') {
 247     vim.enterMode('ignore', {type: 'blacklist'})
 248   }
 249 })
 250 ```
 251
 252 #### The `notification` and `hideNotification` events
 253
 254 The `notification` event occurs when `vim.notify(message)` is called, and means
 255 that `message` should be displayed to the user.
 256
 257 The `hideNotification` event occurs when the `vim.hideNotification()` is called,
 258 and means that the current notification is requested to be hidden.
 259
 260 The data passed to listeners is an object with the following properties:
 261
 262 - vim: The current [vim object].
 263 - message: The message that should be notified. Only for the `notification`
 264   event.
 265
 266 Both of these events are emitted even if the [`notifications_enabled`] option is
 267 disabled, allowing you to display notifications in any way you want.
 268
 269 #### The `modeChange` event
 270
 271 Occurs whenever the current mode in any tab changes. The initial entering of the
 272 default mode in new tabs also counts as a mode change. The data passed to
 273 listeners is the current [vim object].
 274
 275 ```js
 276 vimfx.on('modeChange', vim => {
 277   let mode = vimfx.modes[vim.mode].name
 278   vim.notify(`Entering mode: ${mode}`)
 279 })
 280 ```
 281
 282 #### The `TabSelect` event
 283
 284 Occurs whenever any tab in any window is selected. This is also fired when
 285 Firefox starts for the currently selected tab. The data passed to listeners is
 286 the `event` object passed to the standard Firefox [TabSelect] event.
 287
 288 #### The `modeDisplayChange` event
 289
 290 This is basically a combination of the `modeChange` and the `TabSelect` events.
 291 The event is useful for knowing when to update UI showing the current mode. The
 292 data passed to listeners is the current [vim object].
 293
 294 (VimFx itself uses this event to update the toolbar [button], by setting
 295 `#main-window[vimfx-mode]` to the current mode. You may use this with custom
 296 [styling].)
 297
 298 #### The `focusTypeChange` event
 299
 300 Occurs when focusing or blurring any element. The data passed to listeners is
 301 the current [vim object].
 302
 303 `vim.focusType` has been updated just before this event fires.
 304
 305 (VimFx itself uses this event to update the toolbar [button], by setting
 306 `#main-window[vimfx-focus-type]` to the current focus type. You may use this
 307 with custom [styling].)
 308
 309 #### The `shutdown` event
 310
 311 Occurs when:
 312
 313 - VimFx shuts down: When Firefox shuts down, when VimFx is disabled or when
 314   VimFx is updated.
 315 - When the config file is reloaded using the `zr` command.
 316
 317 If you care about that things you do in `config.js` and `frame.js` are undone
 318 when any of the above happens, read on.
 319
 320 If all you do is using the methods of the `vimfx` object, you shouldn’t need to
 321 care about this event.
 322
 323 The following methods don’t need any undoing:
 324
 325 - `vimfx.get(...)`
 326 - `vimfx.getDefault(...)`
 327 - `vimfx.send(...)`
 328 - `vimfx.off(...)`
 329
 330 The following methods are automatically undone when the `shutdown` event fires.
 331 This means that if you, for example, add a custom command in `config.js` but
 332 then remove it from `config.js` and hit `zr`, the custom command will be gone in
 333 VimFx.
 334
 335 - `vimfx.set(...)`
 336 - `vimfx.addCommand(...)`
 337 - `vimfx.addOptionOverrides(...)`
 338 - `vimfx.addKeyOverrides(...)`
 339 - `vimfx.on(...)`
 340
 341 The following require manual undoing:
 342
 343 - `vimfx.mode`. Any changes you do here must be manually undone.
 344
 345 If you add event listeners in `frame.js`, here’s an example of how to remove
 346 them on `shutdown`:
 347
 348 ```js
 349 // config.js
 350 vimfx.on('shutdown', () => {
 351   Components.classes['@mozilla.org/globalmessagemanager;1']
 352     .getService(Components.interfaces.nsIMessageListenerManager)
 353     // Send this message to _all_ frame scripts.
 354     .broadcastAsyncMessage('VimFx-config:shutdown')
 355 })
 356 ```
 357
 358 ```js
 359 // frame.js
 360 let listeners = []
 361 function listen(eventName, listener) {
 362   addEventListener(eventName, listener, true)
 363   listeners.push([eventName, listener])
 364 }
 365
 366 listen('focus', event => {
 367   console.log('focused element', event.target)
 368 })
 369
 370 addMessageListener('VimFx-config:shutdown', () => {
 371   listeners.forEach(([eventName, listener]) => {
 372     removeMessageListener(eventName, listener, true)
 373   })
 374 })
 375 ```
 376
 377 ### `vimfx.modes`
 378
 379 An object whose keys are mode names and whose values are [mode object]s.
 380
 381 This is a very low-level part of the API. It allows to:
 382
 383 - Access all commands and run them. This is the most common thing that a config
 384   file user needs it for.
 385
 386   ```js
 387     let {commands} = vimfx.modes.normal
 388     // Inside a custom command:
 389     commands.tab_new.run(args)
 390   ```
 391
 392 - Adding new commands. It is recommended to use the `vimfx.addCommand(...)`
 393   helper instead. It’s easier.
 394
 395   ```js
 396   vimfx.modes.normal.commands.new_command = {
 397     pref: 'extensions.my_extension.mode.normal.new_command',
 398     category: 'misc',
 399     order: 10000,
 400     description: translate('mode.normal.new_command'),
 401     run: args => console.log('New command! args:', args)
 402   }
 403   ```
 404
 405 - Adding new modes. This is the most advanced customization you can do to VimFx.
 406   Expect having to read VimFx’s source code to figure it all out.
 407
 408   ```js
 409   vimfx.modes.new_mode = {
 410     name: translate('mode.new_mode'),
 411     order: 10000,
 412     commands: {},
 413     onEnter(args) {},
 414     onLeave(args) {},
 415     onInput(args, match) {
 416       if (match.type === 'full') {
 417         match.command.run(args)
 418       }
 419       return (match.type !== 'none')
 420     },
 421   }
 422   ```
 423
 424 Have a look at [modes.coffee] and [commands.coffee] for more information.
 425
 426 ### `vimfx.get('categories')`
 427
 428 An object whose keys are category names and whose values are [category object]s.
 429
 430 ```js
 431 let categories = vimfx.get('categories')
 432
 433 // Add a new category.
 434 categories.custom = {
 435   name: 'Custom commands',
 436   order: 10000,
 437 }
 438
 439 // Swap the order of the Location and Tabs categories.
 440 ;[commands.focus_location_bar.order, categories.tabs.order] =
 441   [categories.tabs.order, commands.focus_location_bar.order]
 442 ```
 443
 444 ### Mode object
 445
 446 A mode is an object with the following properties:
 447
 448 - name: `String`. A human readable name of the mode used in the Keyboard
 449   Shortcuts help dialog and VimFx’s settings page in the Add-ons Manager. Config
 450   file users adding custom modes could simply use a hard-coded string; extension
 451   authors are encouraged to look up the name from a locale file.
 452 - order: `Number`. The first of the default modes has the order `100` and then
 453   they increase by `100` per mode. This allows to put new modes between two
 454   already existing ones.
 455 - commands: `Object`. The keys are command names and the values are [command
 456   object]s.
 457 - onEnter(data, ...args): `Function`. Called when the mode is entered.
 458 - onLeave(data): `Function`. Called when the mode is left.
 459 - onInput(data, match): `Function`. Called when a key is pressed.
 460
 461 #### onEnter, onLeave and onInput
 462
 463 These methods are called with an object (called `data` above) with the following
 464 properties:
 465
 466 - vim: The current [vim object].
 467 - storage: An object unique to the current [vim object] and to the current mode.
 468   Allows to share things between commands of the same mode by getting and
 469   setting keys on it.
 470
 471 ##### onEnter
 472
 473 This method is called with an object as mentioned above, and after that there
 474 may be any number of arguments (`args` in `vim.enterMode(modeName, ...args)`)
 475 that the mode is free to do whatever it wants with.
 476
 477 Whatever is returned from `onEnter` will be returned from
 478 `vim.enterMode(modeName, ...args)`.
 479
 480 ##### onInput
 481
 482 The object passed to this method (see above) also has the following properties:
 483
 484 - uiEvent: `Event` or `false`. The keydown event object if the event occurred in
 485   the browser UI, `false` otherwise (if the event occurred in web page content).
 486 - count: `Number`. The count for the command. `undefined` if no count. (This is
 487   simply a copy of `match.count`. `match` is defined below.)
 488
 489 The above object should be passed to commands when running them. The mode is
 490 free to do whatever it wants with the return value (if any) of the commands it
 491 runs.
 492
 493 It also receives a [match object] as the second argument.
 494
 495 `onInput` should return `true` if the current keypress should not be passed on
 496 to the browser and web pages, and `false` otherwise.
 497
 498 ### Category object
 499
 500 A category is an object with the following properties:
 501
 502 - name: `String`. A human readable name of the category used in the Keyboard
 503   Shortcuts help dialog and VimFx’s settings page in the Add-ons Manager. Config
 504   file users adding custom categories could simply a use hard-coded string;
 505   extension authors are encouraged to look up the name from a locale file.
 506 - order: `Number`. The first of the default categories is the “uncategorized”
 507   category. It has the order `100` and then they increase by `100` per category.
 508   This allows to put new categories between two already existing ones.
 509
 510 ### Command object
 511
 512 A command is an object with the following properties:
 513
 514 - pref: `String`. The pref used to store the shortcuts for the command.
 515 - run(args): `Function`. Called when the command is activated.
 516 - description: `String`. A description of the command, shown in the Keyboard
 517   Shortcuts help dialog and VimFx’s settings page in the Add-ons Manager. Config
 518   file users adding custom commands could simply use a hard-coded string;
 519   extension authors are encouraged to look up the name from a locale file.
 520 - category: `String`. The category to add the command to. The value has to be
 521   one of the keys of [`vimfx.get('categories')`][categories].
 522 - order: `Number`. The first of the default commands has the order `100` and
 523   then they increase by `100` per command. This allows to put new commands
 524   between two already existing ones.
 525
 526 ### Match object
 527
 528 A `match` object has the following properties:
 529
 530 - type: `String`. It has one of the following values:
 531
 532   - `'full'`: The current keypress, together with previous keypresses, fully
 533     matches a command shortcut.
 534   - `'partial'`: The current keypress, together with previous keypresses,
 535     partially matches a command shortcut.
 536   - `'count'`: The current keypress is not part of a command shortcut, but is a
 537     digit and contributes to the count of a future matched command.
 538   - `'none'`: The current keypress is not part of a command shortcut and does
 539     not contribute to a count.
 540
 541 - likelyConflict: `Boolean`. This is `true` if the current keypress is likely to
 542   cause conflicts with default Firefox behavior of that key, and `false`
 543   otherwise. A mode might not want to run commands and suppress the event if
 544   this value is `true`. VimFx uses the current keypress and `vim.focusType` of
 545   the current [vim object] to decide if the current keypress is a likely
 546   conflict:
 547
 548   1. If the key is part of the tail of a shortcut, it is never a conflict.
 549   2. If `vim.focusType` is `'activatable'` or `'adjustable'` and the key is
 550      present in [`activatable_element_keys`] or [`adjustable_element_keys`]
 551      (respectively), then it is a likely conflict.
 552   3. Finally, unless `vim.focusType` is `'none'`, then it is a likely conflict.
 553      This most commonly means that a text input is focused.
 554
 555   Note that any VimFx shortcut starting with a keypress involving a modifier is
 556   _very_ likely to conflict with either a Firefox default shortcut or a shortcut
 557   from some other add-on. This is _not_ attempted to be detected in any way.
 558   Instead, VimFx uses no modifiers in any default Normal mode shortcuts, leaving
 559   it up to you to choose modifier-shortcuts that work out for you if you want
 560   such shortcuts. In other words, for modifier-shortcuts the point of VimFx _is_
 561   to conflict (overriding default shortcuts).
 562
 563 - command: `null` unless `type` is `'full'`. Then it is the matched command (a
 564   [command object]).
 565
 566   The matched command should usually be run at this point. It is suitable to
 567   pass on the object passed to [onInput] to the command. Some modes might choose
 568   to add extra properties to the object first. (That is favored over passing
 569   several arguments, since it makes it easier for the command to in turn pass
 570   the same data it got on to another command, if needed.)
 571
 572   Usually the return value of the command isn’t used, but that’s up to the mode.
 573
 574 - count: `Number`. The count for the command. `undefined` if no count.
 575
 576 - specialKeys: `Object`. The keys may be any of the following:
 577
 578   - `<force>`
 579   - `<late>`
 580
 581   If a key exists, its value is always `true`. The keys that exist indicate the
 582   [special keys] for the sequence used for the matched command (if any).
 583
 584 - keyStr: `String`. The current keypress represented as a string.
 585
 586 - unmodifiedKey: `String`. `keyStr` without modifiers.
 587
 588 - toplevel: `Boolean`. Whether or not the match was a toplevel match in the
 589   shortcut key tree. This is `true` unless the match is part of the tail of a
 590   multi-key shortcut.
 591
 592 - discard(): `Function`. Discards keys pressed so far: If `type` is `'partial'`
 593   or `'count'`. For example, if you have typed `12g`, run `match.discard()` and
 594   then press `$`, the `$` command will be run instead of `12g$`.
 595
 596 ### Vim object
 597
 598 There is one `vim` object per tab.
 599
 600 A `vim` object has the following properties:
 601
 602 - window: [`Window`]. The current Firefox window object. Most commands
 603   interacting with Firefox’s UI use this.
 604
 605 - browser: [`Browser`]. The `browser` that this vim object handles.
 606
 607 - options: `Object`. Provides access to all of VimFx’s options. It is an
 608   [options object].
 609
 610 - mode: `String`. The current mode name.
 611
 612 - focusType: `String`. The type of currently focused element. VimFx decides the
 613   type based on how it responds to keystorkes. It has one of the following
 614   values:
 615
 616   - `'ignore'`: Some kind of Vim-style editor. VimFx automatically
 617     enters Ignore mode when this focus type is encountered.
 618   - `'editable'`: Some kind of text input, a `<select>` element or a
 619     “contenteditable” element.
 620   - `'activatable'`: An “activatable” element (link or button).
 621     (See also the [`activatable_element_keys`] option.)
 622   - `'adjustable'`: An “adjustable” element (form control or video
 623     player). (See also the [`adjustable_element_keys`] option.)
 624   - `'other'`: Some other kind of element that can receive keystrokes.
 625     (Deprecated.)
 626   - `'none'`: The currently focused element does not appear to respond to
 627     keystrokes in any special way.
 628
 629   [The `focusTypeChange` event] is fired whenever `focusType` is updated.
 630
 631   `match.likelyConflict` of [match object]s depend on `focusType`.
 632
 633 - enterMode(modeName, ...args): `Function`. Enter mode `modeName`, passing
 634   `...args` to the mode. It is up to every mode to do whatever it wants to with
 635   `...args`. If `modeName` was already the current mode, nothing is done and
 636   `undefined` is returned. Otherwise it us up to the mode to return whatever it
 637   wants to.
 638
 639 - isUIEvent(event): `Function`. Returns `true` if `event` occurred in the
 640   browser UI, and `false` otherwise (if it occurred in web page content).
 641
 642 - notify(message): `Function`. Display a notification with the text `message`.
 643
 644 - hideNotification(): `Function`. Hide the current notification (if any).
 645
 646 - markPageInteraction(value=true): `Function`. When `value` is `true` (as it is
 647   by default when the argument is omitted), marks that the user has interacted
 648   with the page. After that [autofocus prevention] is not done anymore. Commands
 649   interacting with web page content might want to do this. If `value` is
 650   `false`, the state is reset and autofocus prevention _will_ be done again.
 651
 652 **Warning:** There are also properties starting with an underscore on `vim`
 653 objects. They are private, and not supposed to be used outside of VimFx’s own
 654 source code. They may change at any time.
 655
 656 ### Options object
 657
 658 An `options` object provides access to all of VimFx’s options. It is an object
 659 whose keys are VimFx pref names.
 660
 661 Note that the values are not just simply `vimfx.get(pref)` for the `pref` in
 662 question; they are _parsed_ (`parse(vimfx.get(pref))`):
 663
 664 - Space-separated prefs are parsed into arrays of strings.
 665
 666 - `black_list` and `{prev,next}_patterns` are parsed into arrays of regular
 667   expressions.
 668
 669 (See [parse-prefs.coffee] for all details.)
 670
 671 Any [option overrides] are automatically taken into account when getting an
 672 option value.
 673
 674 The [special options] are also available on this object.
 675
 676
 677 ### Location object
 678
 679 A location object is very similar to [`window.location`] in web pages.
 680 Technically, it is a [`URL`] instance. You can experiment with the current
 681 location object by opening the [web console] and entering `location`.
 682
 683
 684 ## `frame.js` API
 685
 686 In `frame.js`, the following API is available as the variable `vimfx`.
 687
 688 ### `vimfx.listen(message, listener)`
 689
 690 Listen for `message` (a string) from `config.js`. `listener` will be called with
 691 the data sent from `config.js` (if any), and optionally a callback function if
 692 `config.js` wants you to respond. If so, call the callback function, optionally
 693 with some data to send back to `config.js.` `config.js` uses its
 694 [`vimfx.send(...)`] method to send  `message` (and optionally some data along
 695 with it).
 696
 697 See the [`vimfx.send(...)`] method in `config.js` for more information and
 698 examples.
 699
 700 ### `vimfx.setHintMatcher(hintMatcher)`
 701
 702 `hintMatcher` is a function that lets you customize which elements do and don’t
 703 get hints. It might help to read about [the `f` commands] first.
 704
 705 If you call `vimfx.setHintMatcher(hintMatcher)` more than once, only the
 706 `hintMatcher` provided the last time will be used.
 707
 708 ```js
 709 vimfx.setHintMatcher((id, element, {type, semantic}) => {
 710   // Inspect `element` and change `type` and `semantic` if needed.
 711   return {type, semantic}
 712 })
 713 ```
 714
 715 The arguments passed to the `hintMatcher` function are:
 716
 717 - id: `String`. A string identifying which command is used:
 718
 719   - `'normal'`: `f` or `af`.
 720   - `'tab'`: `F`, `gf` or `gF`.
 721   - `'copy'`: `yf`.
 722   - `'focus'`: `zf`.
 723
 724 - element: `Element`. One out of all elements currently inside the viewport.
 725
 726 - info: `Object`. It has the following properties:
 727
 728   - type: `String` or `null`. If a string, it means that `element` should get a
 729     hint. If `null`, it won’t. See the available strings below. When a marker
 730     is matched, `type` decides what happens to `element`.
 731   - semantic: `Boolean`. Indicates whether or not the element is “semantic.”
 732     Semantic elements get better hints.
 733
 734   This object contains information on how VimFx has matched `element`. You have
 735   the opportunity to change this.
 736
 737 The available type strings depend on `id`:
 738
 739 - normal:
 740
 741   - link: A “proper” link (not used as a button with the help of JavaScript),
 742     with an `href` attribute.
 743   - text: An element that can you can type in, such as text inputs.
 744   - clickable: Some clickable element not falling into another category.
 745   - clickable-special: Like “clickable,” but uses a different technique to
 746     simulate a click on the element. If “clickable” doesn’t work, try this one.
 747   - scrollable: A scrollable element.
 748
 749 - tab:
 750
 751   - link: Like “link” when `id` is “normal” (see above).
 752
 753 - copy:
 754
 755   - link: Like “link” when `id` is “normal” (see above).
 756   - text: Like “text” when `id` is “normal” (see above), except that in this
 757     case “contenteditable” elements are not included.
 758   - contenteditable: Elements with “contenteditable” turned on.
 759
 760 - focus:
 761
 762   - focusable: Any focusable element not falling into another category.
 763   - scrollable: Like “scrollable” when `id` is “normal” (see above).
 764
 765 The function must return an object like the `info` parameter (with the `type`
 766 and `semantic` properties).
 767
 768
 769 ## Stability
 770
 771 The API is currently **experimental** and therefore **unstable.** Things might
 772 break with new VimFx versions. However, no breaking changes are planned, and
 773 will be avoided if feasible.
 774
 775 As soon as VimFx 1.0.0 (which does not seem to be too far away) is released
 776 backwards compatibility will be a priority and won’t be broken until VimFx
 777 2.0.0.
 778
 779 [option overrides]: #vimfxaddoptionoverridesrules
 780 [`vimfx.send(...)`]: #vimfxsendvim-message-data--null-callback--null
 781 [`vimfx.listen(...)`]: #vimfxlistenmessage-listener
 782 [categories]: #vimfxgetcategories
 783 [`vimfx.modes`]: #vimfxmodes
 784 [onInput]: #oninput
 785 [mode object]: #mode-object
 786 [category object]: #category-object
 787 [command object]: #command-object
 788 [match object]: #match-object
 789 [vim object]: #vim-object
 790 [options object]: #options-object
 791 [location object]: #location-object
 792 [The `focusTypeChange` event]: #the-focustypechange-event
 793 [the `shutdown` event]: #the-shutdown-event
 794
 795 [blacklisted]: options.md#blacklist
 796 [special options]: options.md#special-options
 797 [config file]: config-file.md
 798 [bootstrap.js]: config-file.md#bootstrapjs
 799 [autofocus prevention]: options.md#prevent-autofocus
 800 [`activatable_element_keys`]: options.md#activatable_element_keys
 801 [`adjustable_element_keys`]: options.md#adjustable_element_keys
 802 [`notifications_enabled`]: options.md#notifications_enabled
 803
 804 [button]: button.md
 805 [the `f` commands]: commands.md#the-f-commands--hints-mode
 806 [special keys]: shortcuts.md#special-keys
 807 [styling]: styling.md
 808
 809 [defaults.coffee]: ../extension/lib/defaults.coffee
 810 [parse-prefs.coffee]: ../extension/lib/parse-prefs.coffee
 811 [modes.coffee]: ../extension/lib/modes.coffee
 812 [commands.coffee]: ../extension/lib/commands.coffee
 813 [vim.coffee]: ../extension/lib/vim.coffee
 814
 815 [`Window`]: https://developer.mozilla.org/en-US/docs/Web/API/Window
 816 [`Browser`]: https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XUL/browser
 817 [`window.location`]: https://developer.mozilla.org/en-US/docs/Web/API/Location
 818 [`URL`]: https://developer.mozilla.org/en-US/docs/Web/API/URL
 819 [Message Manager]: https://developer.mozilla.org/en-US/Firefox/Multiprocess_Firefox/Message_Manager
 820 [TabSelect]: https://developer.mozilla.org/en-US/docs/Web/Events/TabSelect
 821 [web console]: https://developer.mozilla.org/en-US/docs/Tools/Web_Console
 822 [about:config]: http://kb.mozillazine.org/About:config