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, where `data` is an object. Which properties `data`
 224 has is specific to each event.
 225
 226 You may use `vimfx.off(eventName, listener)` if you’d like to remove your
 227 added listener for some reason.
 228
 229 While [`vimfx.send(...)`] and [`vimfx.listen(...)`] are all about passing
 230 messages between `config.js` and `frame.js`, `vimfx.on(...)` is all about doing
 231 something whenever VimFx emits internal events.
 232
 233 #### The `locationChange` event
 234
 235 Occurs when opening a new tab, navigating to a new URL or refreshing the page,
 236 causing a full page load.
 237
 238 `data`:
 239
 240 - vim: The current [vim object].
 241 - location: A [location object].
 242
 243 This event can be used to enter a different mode by default on some pages (which
 244 can be used to replace the blacklist option).
 245
 246 ```js
 247 vimfx.on('locationChange', ({vim, location}) => {
 248   if (location.hostname === 'example.com') {
 249     vim.enterMode('ignore', {type: 'blacklist'})
 250   }
 251 })
 252 ```
 253
 254 #### The `notification` and `hideNotification` events
 255
 256 The `notification` event occurs when `vim.notify(message)` is called, and means
 257 that `message` should be displayed to the user.
 258
 259 The `hideNotification` event occurs when the `vim.hideNotification()` is called,
 260 and means that the current notification is requested to be hidden.
 261
 262 `data`:
 263
 264 - vim: The current [vim object].
 265 - message: The message that should be notified. Only for the `notification`
 266   event.
 267
 268 Both of these events are emitted even if the [`notifications_enabled`] option is
 269 disabled, allowing you to display notifications in any way you want.
 270
 271 #### The `modeChange` event
 272
 273 Occurs whenever the current mode in any tab changes. The initial entering of the
 274 default mode in new tabs also counts as a mode change.
 275
 276 `data`:
 277
 278 - vim: The current [vim object].
 279
 280 ```js
 281 vimfx.on('modeChange', ({vim}) => {
 282   let mode = vimfx.modes[vim.mode].name
 283   vim.notify(`Entering mode: ${mode}`)
 284 })
 285 ```
 286
 287 #### The `TabSelect` event
 288
 289 Occurs whenever any tab in any window is selected. This is also fired when
 290 Firefox starts for the currently selected tab.
 291
 292 `data`:
 293
 294 - event: The `event` object passed to the standard Firefox [TabSelect] event.
 295
 296 #### The `modeDisplayChange` event
 297
 298 This is basically a combination of the `modeChange` and the `TabSelect` events.
 299 The event is useful for knowing when to update UI showing the current mode.
 300
 301 `data`:
 302
 303 - vim: The current [vim object].
 304
 305 (VimFx itself uses this event to update the toolbar [button], by setting
 306 `#main-window[vimfx-mode]` to the current mode. You may use this with custom
 307 [styling].)
 308
 309 #### The `focusTypeChange` event
 310
 311 Occurs when focusing or blurring any element. See also the [`blur_timeout`]
 312 pref.
 313
 314 `data`:
 315
 316 - vim: The current [vim object].
 317
 318 `data.vim.focusType` has been updated just before this event fires.
 319
 320 (VimFx itself uses this event to update the toolbar [button], by setting
 321 `#main-window[vimfx-focus-type]` to the current focus type. You may use this
 322 with custom [styling].)
 323
 324 #### The `shutdown` event
 325
 326 Occurs when:
 327
 328 - VimFx shuts down: When Firefox shuts down, when VimFx is disabled or when
 329   VimFx is updated.
 330 - When the config file is reloaded using the `zr` command.
 331
 332 `data`: No data at all is passed.
 333
 334 If you care about that things you do in `config.js` and `frame.js` are undone
 335 when any of the above happens, read on.
 336
 337 If all you do is using the methods of the `vimfx` object, you shouldn’t need to
 338 care about this event.
 339
 340 The following methods don’t need any undoing:
 341
 342 - `vimfx.get(...)`
 343 - `vimfx.getDefault(...)`
 344 - `vimfx.send(...)`
 345 - `vimfx.off(...)`
 346
 347 The following methods are automatically undone when the `shutdown` event fires.
 348 This means that if you, for example, add a custom command in `config.js` but
 349 then remove it from `config.js` and hit `zr`, the custom command will be gone in
 350 VimFx.
 351
 352 - `vimfx.set(...)`
 353 - `vimfx.addCommand(...)`
 354 - `vimfx.addOptionOverrides(...)`
 355 - `vimfx.addKeyOverrides(...)`
 356 - `vimfx.on(...)`
 357
 358 The following require manual undoing:
 359
 360 - `vimfx.mode`. Any changes you do here must be manually undone.
 361
 362 If you add event listeners in `frame.js`, here’s an example of how to remove
 363 them on `shutdown`:
 364
 365 ```js
 366 // config.js
 367 vimfx.on('shutdown', () => {
 368   Components.classes['@mozilla.org/globalmessagemanager;1']
 369     .getService(Components.interfaces.nsIMessageListenerManager)
 370     // Send this message to _all_ frame scripts.
 371     .broadcastAsyncMessage('VimFx-config:shutdown')
 372 })
 373 ```
 374
 375 ```js
 376 // frame.js
 377 let listeners = []
 378 function listen(eventName, listener) {
 379   addEventListener(eventName, listener, true)
 380   listeners.push([eventName, listener])
 381 }
 382
 383 listen('focus', event => {
 384   console.log('focused element', event.target)
 385 })
 386
 387 addMessageListener('VimFx-config:shutdown', () => {
 388   listeners.forEach(([eventName, listener]) => {
 389     removeMessageListener(eventName, listener, true)
 390   })
 391 })
 392 ```
 393
 394 ### `vimfx.modes`
 395
 396 An object whose keys are mode names and whose values are [mode object]s.
 397
 398 This is a very low-level part of the API. It allows to:
 399
 400 - Access all commands and run them. This is the most common thing that a config
 401   file user needs it for.
 402
 403   ```js
 404     let {commands} = vimfx.modes.normal
 405     // Inside a custom command:
 406     commands.tab_new.run(args)
 407   ```
 408
 409 - Adding new commands. It is recommended to use the `vimfx.addCommand(...)`
 410   helper instead. It’s easier.
 411
 412   ```js
 413   vimfx.modes.normal.commands.new_command = {
 414     pref: 'extensions.my_extension.mode.normal.new_command',
 415     category: 'misc',
 416     order: 10000,
 417     description: translate('mode.normal.new_command'),
 418     run: args => console.log('New command! args:', args)
 419   }
 420   ```
 421
 422 - Adding new modes. This is the most advanced customization you can do to VimFx.
 423   Expect having to read VimFx’s source code to figure it all out.
 424
 425   ```js
 426   vimfx.modes.new_mode = {
 427     name: translate('mode.new_mode'),
 428     order: 10000,
 429     commands: {},
 430     onEnter(args) {},
 431     onLeave(args) {},
 432     onInput(args, match) {
 433       if (match.type === 'full') {
 434         match.command.run(args)
 435       }
 436       return (match.type !== 'none')
 437     },
 438   }
 439   ```
 440
 441 Have a look at [modes.coffee] and [commands.coffee] for more information.
 442
 443 ### `vimfx.get('categories')`
 444
 445 An object whose keys are category names and whose values are [category object]s.
 446
 447 ```js
 448 let categories = vimfx.get('categories')
 449
 450 // Add a new category.
 451 categories.custom = {
 452   name: 'Custom commands',
 453   order: 10000,
 454 }
 455
 456 // Swap the order of the Location and Tabs categories.
 457 ;[commands.focus_location_bar.order, categories.tabs.order] =
 458   [categories.tabs.order, commands.focus_location_bar.order]
 459 ```
 460
 461 ### Mode object
 462
 463 A mode is an object with the following properties:
 464
 465 - name: `String`. A human readable name of the mode used in the Keyboard
 466   Shortcuts help dialog and VimFx’s settings page in the Add-ons Manager. Config
 467   file users adding custom modes could simply use a hard-coded string; extension
 468   authors are encouraged to look up the name from a locale file.
 469 - order: `Number`. The first of the default modes has the order `100` and then
 470   they increase by `100` per mode. This allows to put new modes between two
 471   already existing ones.
 472 - commands: `Object`. The keys are command names and the values are [command
 473   object]s.
 474 - onEnter(data, ...args): `Function`. Called when the mode is entered.
 475 - onLeave(data): `Function`. Called when the mode is left.
 476 - onInput(data, match): `Function`. Called when a key is pressed.
 477
 478 #### onEnter, onLeave and onInput
 479
 480 These methods are called with an object (called `data` above) with the following
 481 properties:
 482
 483 - vim: The current [vim object].
 484 - storage: An object unique to the current [vim object] and to the current mode.
 485   Allows to share things between commands of the same mode by getting and
 486   setting keys on it.
 487
 488 ##### onEnter
 489
 490 This method is called with an object as mentioned above, and after that there
 491 may be any number of arguments (`args` in `vim.enterMode(modeName, ...args)`)
 492 that the mode is free to do whatever it wants with.
 493
 494 Whatever is returned from `onEnter` will be returned from
 495 `vim.enterMode(modeName, ...args)`.
 496
 497 ##### onInput
 498
 499 The object passed to this method (see above) also has the following properties:
 500
 501 - uiEvent: `Event` or `false`. The keydown event object if the event occurred in
 502   the browser UI, `false` otherwise (if the event occurred in web page content).
 503 - count: `Number`. The count for the command. `undefined` if no count. (This is
 504   simply a copy of `match.count`. `match` is defined below.)
 505
 506 The above object should be passed to commands when running them. The mode is
 507 free to do whatever it wants with the return value (if any) of the commands it
 508 runs.
 509
 510 It also receives a [match object] as the second argument.
 511
 512 `onInput` should return `true` if the current keypress should not be passed on
 513 to the browser and web pages, and `false` otherwise.
 514
 515 ### Category object
 516
 517 A category is an object with the following properties:
 518
 519 - name: `String`. A human readable name of the category used in the Keyboard
 520   Shortcuts help dialog and VimFx’s settings page in the Add-ons Manager. Config
 521   file users adding custom categories could simply a use hard-coded string;
 522   extension authors are encouraged to look up the name from a locale file.
 523 - order: `Number`. The first of the default categories is the “uncategorized”
 524   category. It has the order `100` and then they increase by `100` per category.
 525   This allows to put new categories between two already existing ones.
 526
 527 ### Command object
 528
 529 A command is an object with the following properties:
 530
 531 - pref: `String`. The pref used to store the shortcuts for the command.
 532 - run(args): `Function`. Called when the command is activated.
 533 - description: `String`. A description of the command, shown in the Keyboard
 534   Shortcuts help dialog and VimFx’s settings page in the Add-ons Manager. Config
 535   file users adding custom commands could simply use a hard-coded string;
 536   extension authors are encouraged to look up the name from a locale file.
 537 - category: `String`. The category to add the command to. The value has to be
 538   one of the keys of [`vimfx.get('categories')`][categories].
 539 - order: `Number`. The first of the default commands has the order `100` and
 540   then they increase by `100` per command. This allows to put new commands
 541   between two already existing ones.
 542
 543 ### Match object
 544
 545 A `match` object has the following properties:
 546
 547 - type: `String`. It has one of the following values:
 548
 549   - `'full'`: The current keypress, together with previous keypresses, fully
 550     matches a command shortcut.
 551   - `'partial'`: The current keypress, together with previous keypresses,
 552     partially matches a command shortcut.
 553   - `'count'`: The current keypress is not part of a command shortcut, but is a
 554     digit and contributes to the count of a future matched command.
 555   - `'none'`: The current keypress is not part of a command shortcut and does
 556     not contribute to a count.
 557
 558 - likelyConflict: `Boolean`. This is `true` if the current keypress is likely to
 559   cause conflicts with default Firefox behavior of that key, and `false`
 560   otherwise. A mode might not want to run commands and suppress the event if
 561   this value is `true`. VimFx uses the current keypress and `vim.focusType` of
 562   the current [vim object] to decide if the current keypress is a likely
 563   conflict:
 564
 565   1. If the key is part of the tail of a shortcut, it is never a conflict.
 566   2. If `vim.focusType` is `'activatable'` or `'adjustable'` and the key is
 567      present in [`activatable_element_keys`] or [`adjustable_element_keys`]
 568      (respectively), then it is a likely conflict.
 569   3. Finally, unless `vim.focusType` is `'none'`, then it is a likely conflict.
 570      This most commonly means that a text input is focused.
 571
 572   Note that any VimFx shortcut starting with a keypress involving a modifier is
 573   _very_ likely to conflict with either a Firefox default shortcut or a shortcut
 574   from some other add-on. This is _not_ attempted to be detected in any way.
 575   Instead, VimFx uses no modifiers in any default Normal mode shortcuts, leaving
 576   it up to you to choose modifier-shortcuts that work out for you if you want
 577   such shortcuts. In other words, for modifier-shortcuts the point of VimFx _is_
 578   to conflict (overriding default shortcuts).
 579
 580 - command: `null` unless `type` is `'full'`. Then it is the matched command (a
 581   [command object]).
 582
 583   The matched command should usually be run at this point. It is suitable to
 584   pass on the object passed to [onInput] to the command. Some modes might choose
 585   to add extra properties to the object first. (That is favored over passing
 586   several arguments, since it makes it easier for the command to in turn pass
 587   the same data it got on to another command, if needed.)
 588
 589   Usually the return value of the command isn’t used, but that’s up to the mode.
 590
 591 - count: `Number`. The count for the command. `undefined` if no count.
 592
 593 - specialKeys: `Object`. The keys may be any of the following:
 594
 595   - `<force>`
 596   - `<late>`
 597
 598   If a key exists, its value is always `true`. The keys that exist indicate the
 599   [special keys] for the sequence used for the matched command (if any).
 600
 601 - keyStr: `String`. The current keypress represented as a string.
 602
 603 - unmodifiedKey: `String`. `keyStr` without modifiers.
 604
 605 - toplevel: `Boolean`. Whether or not the match was a toplevel match in the
 606   shortcut key tree. This is `true` unless the match is part of the tail of a
 607   multi-key shortcut.
 608
 609 - discard(): `Function`. Discards keys pressed so far: If `type` is `'partial'`
 610   or `'count'`. For example, if you have typed `12g`, run `match.discard()` and
 611   then press `$`, the `$` command will be run instead of `12g$`.
 612
 613 ### Vim object
 614
 615 There is one `vim` object per tab.
 616
 617 A `vim` object has the following properties:
 618
 619 - window: [`Window`]. The current Firefox window object. Most commands
 620   interacting with Firefox’s UI use this.
 621
 622 - browser: [`Browser`]. The `browser` that this vim object handles.
 623
 624 - options: `Object`. Provides access to all of VimFx’s options. It is an
 625   [options object].
 626
 627 - mode: `String`. The current mode name.
 628
 629 - focusType: `String`. The type of currently focused element. VimFx decides the
 630   type based on how it responds to keystorkes. It has one of the following
 631   values:
 632
 633   - `'ignore'`: Some kind of Vim-style editor. VimFx automatically
 634     enters Ignore mode when this focus type is encountered.
 635   - `'editable'`: Some kind of text input, a `<select>` element or a
 636     “contenteditable” element.
 637   - `'activatable'`: An “activatable” element (link or button).
 638     (See also the [`activatable_element_keys`] option.)
 639   - `'adjustable'`: An “adjustable” element (form control or video
 640     player). (See also the [`adjustable_element_keys`] option.)
 641   - `'findbar'`: The findbar text input is focused.
 642   - `'none'`: The currently focused element does not appear to respond to
 643     keystrokes in any special way.
 644
 645   [The `focusTypeChange` event] is fired whenever `focusType` is updated.
 646
 647   `match.likelyConflict` of [match object]s depend on `focusType`.
 648
 649 - enterMode(modeName, ...args): `Function`. Enter mode `modeName`, passing
 650   `...args` to the mode. It is up to every mode to do whatever it wants to with
 651   `...args`. If `modeName` was already the current mode, nothing is done and
 652   `undefined` is returned. Otherwise it us up to the mode to return whatever it
 653   wants to.
 654
 655 - isUIEvent(event): `Function`. Returns `true` if `event` occurred in the
 656   browser UI, and `false` otherwise (if it occurred in web page content).
 657
 658 - notify(message): `Function`. Display a notification with the text `message`.
 659
 660 - hideNotification(): `Function`. Hide the current notification (if any).
 661
 662 - markPageInteraction(value=true): `Function`. When `value` is `true` (as it is
 663   by default when the argument is omitted), marks that the user has interacted
 664   with the page. After that [autofocus prevention] is not done anymore. Commands
 665   interacting with web page content might want to do this. If `value` is
 666   `false`, the state is reset and autofocus prevention _will_ be done again.
 667
 668 **Warning:** There are also properties starting with an underscore on `vim`
 669 objects. They are private, and not supposed to be used outside of VimFx’s own
 670 source code. They may change at any time.
 671
 672 ### Options object
 673
 674 An `options` object provides access to all of VimFx’s options. It is an object
 675 whose keys are VimFx pref names.
 676
 677 Note that the values are not just simply `vimfx.get(pref)` for the `pref` in
 678 question; they are _parsed_ (`parse(vimfx.get(pref))`):
 679
 680 - Space-separated prefs are parsed into arrays of strings.
 681
 682 - `blacklist` and `{prev,next}_patterns` are parsed into arrays of regular
 683   expressions.
 684
 685 (See [parse-prefs.coffee] for all details.)
 686
 687 Any [option overrides] are automatically taken into account when getting an
 688 option value.
 689
 690 The [special options] are also available on this object.
 691
 692
 693 ### Location object
 694
 695 A location object is very similar to [`window.location`] in web pages.
 696 Technically, it is a [`URL`] instance. You can experiment with the current
 697 location object by opening the [web console] and entering `location`.
 698
 699
 700 ## `frame.js` API
 701
 702 In `frame.js`, the following API is available as the variable `vimfx`.
 703
 704 ### `vimfx.listen(message, listener)`
 705
 706 Listen for `message` (a string) from `config.js`. `listener` will be called with
 707 the data sent from `config.js` (if any), and optionally a callback function if
 708 `config.js` wants you to respond. If so, call the callback function, optionally
 709 with some data to send back to `config.js.` `config.js` uses its
 710 [`vimfx.send(...)`] method to send  `message` (and optionally some data along
 711 with it).
 712
 713 See the [`vimfx.send(...)`] method in `config.js` for more information and
 714 examples.
 715
 716 ### `vimfx.setHintMatcher(hintMatcher)`
 717
 718 `hintMatcher` is a function that lets you customize which elements do and don’t
 719 get hints. It might help to read about [the `f` commands] first.
 720
 721 If you call `vimfx.setHintMatcher(hintMatcher)` more than once, only the
 722 `hintMatcher` provided the last time will be used.
 723
 724 ```js
 725 vimfx.setHintMatcher((id, element, type) => {
 726   // Inspect `element` and return a different `type` if needed.
 727   return type
 728 })
 729 ```
 730
 731 The arguments passed to the `hintMatcher` function are:
 732
 733 - id: `String`. A string identifying which command is used:
 734
 735   - `'normal'`: `f` or `af`.
 736   - `'tab'`: `F`, `gf` or `gF`.
 737   - `'copy'`: `yf`.
 738   - `'focus'`: `zf`.
 739   - `'select'`: `v`, `zv` or `yv`.
 740
 741 - element: `Element`. One out of all elements currently inside the viewport.
 742
 743 - type: `String` or `null`. If a string, it means that `element` should get a
 744   hint. If `null`, it won’t. See the available strings below. When a marker
 745   is matched, `type` decides what happens to `element`.
 746
 747   This parameter tells how VimFx has matched `element`. You have the opportunity
 748   to change that.
 749
 750 The available type strings depend on `id`:
 751
 752 - normal:
 753
 754   - link: A “proper” link (not used as a button with the help of JavaScript),
 755     with an `href` attribute.
 756   - text: An element that can you can type in, such as text inputs.
 757   - clickable: Some clickable element not falling into another category.
 758   - clickable-special: Like “clickable,” but uses a different technique to
 759     simulate a click on the element. If “clickable” doesn’t work, try this one.
 760   - scrollable: A scrollable element.
 761
 762 - tab:
 763
 764   - link: Like “link” when `id` is “normal” (see above).
 765
 766 - copy:
 767
 768   - link: Like “link” when `id` is “normal” (see above).
 769   - text: Like “text” when `id` is “normal” (see above), except that in this
 770     case “contenteditable” elements are not included.
 771   - contenteditable: Elements with “contenteditable” turned on.
 772
 773 - focus:
 774
 775   - focusable: Any focusable element not falling into another category.
 776   - scrollable: Like “scrollable” when `id` is “normal” (see above).
 777
 778 - select:
 779
 780   - selectable: An element with selectable text (but not text inputs).
 781
 782 The function must return `null` or a string like the `type` parameter.
 783
 784
 785 ## Stability
 786
 787 The API is currently **experimental** and therefore **unstable.** Things might
 788 break with new VimFx versions. However, no breaking changes are planned, and
 789 will be avoided if feasible.
 790
 791 As soon as VimFx 1.0.0 (which does not seem to be too far away) is released
 792 backwards compatibility will be a priority and won’t be broken until VimFx
 793 2.0.0.
 794
 795 [option overrides]: #vimfxaddoptionoverridesrules
 796 [`vimfx.send(...)`]: #vimfxsendvim-message-data--null-callback--null
 797 [`vimfx.listen(...)`]: #vimfxlistenmessage-listener
 798 [categories]: #vimfxgetcategories
 799 [`vimfx.modes`]: #vimfxmodes
 800 [onInput]: #oninput
 801 [mode object]: #mode-object
 802 [category object]: #category-object
 803 [command object]: #command-object
 804 [match object]: #match-object
 805 [vim object]: #vim-object
 806 [options object]: #options-object
 807 [location object]: #location-object
 808 [The `focusTypeChange` event]: #the-focustypechange-event
 809 [the `shutdown` event]: #the-shutdown-event
 810
 811 [blacklisted]: options.md#blacklist
 812 [special options]: options.md#special-options
 813 [config file]: config-file.md
 814 [bootstrap.js]: config-file.md#bootstrapjs
 815 [autofocus prevention]: options.md#prevent-autofocus
 816 [`activatable_element_keys`]: options.md#activatable_element_keys
 817 [`adjustable_element_keys`]: options.md#adjustable_element_keys
 818 [`blur_timeout`]: options.md#blur_timeout
 819 [`notifications_enabled`]: options.md#notifications_enabled
 820
 821 [button]: button.md
 822 [the `f` commands]: commands.md#the-f-commands--hints-mode
 823 [special keys]: shortcuts.md#special-keys
 824 [styling]: styling.md
 825
 826 [defaults.coffee]: ../extension/lib/defaults.coffee
 827 [parse-prefs.coffee]: ../extension/lib/parse-prefs.coffee
 828 [modes.coffee]: ../extension/lib/modes.coffee
 829 [commands.coffee]: ../extension/lib/commands.coffee
 830 [vim.coffee]: ../extension/lib/vim.coffee
 831
 832 [`Window`]: https://developer.mozilla.org/en-US/docs/Web/API/Window
 833 [`Browser`]: https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XUL/browser
 834 [`window.location`]: https://developer.mozilla.org/en-US/docs/Web/API/Location
 835 [`URL`]: https://developer.mozilla.org/en-US/docs/Web/API/URL
 836 [Message Manager]: https://developer.mozilla.org/en-US/Firefox/Multiprocess_Firefox/Message_Manager
 837 [TabSelect]: https://developer.mozilla.org/en-US/docs/Web/Events/TabSelect
 838 [web console]: https://developer.mozilla.org/en-US/docs/Tools/Web_Console
 839 [about:config]: http://kb.mozillazine.org/About:config