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