modules/help.js

   1 /**
   2  * (C) Copyright 2008 Jeremy Maitin-Shepard
   3  * (C) Copyright 2008 Nelson Elhage
   4  * (C) Copyright 2008 David Glasser
   5  * (C) Copyright 2009 John J. Foerch
   6  *
   7  * Use, modification, and distribution are subject to the terms specified in the
   8  * COPYING file.
   9 **/
  10
  11 require("special-buffer.js");
  12 require("interactive.js");
  13
  14 function where_is_command (buffer, command) {
  15     var keymaps = get_current_keymaps(buffer.window);
  16     var list = keymap_lookup_command(keymaps, command);
  17     var msg;
  18     if (list.length == 0)
  19         msg = command + " is not on any key";
  20     else
  21         msg = command + " is on " + list.join(", ");
  22     buffer.window.minibuffer.message(msg);
  23 }
  24 interactive("where-is", null, function (I) {
  25     where_is_command(I.buffer,
  26                      (yield I.minibuffer.read_command($prompt = "Where is command:")));
  27 });
  28
  29 function help_document_generator (document, buffer) {
  30     dom_generator.call(this, document, XHTML_NS);
  31     this.buffer = buffer;
  32 }
  33 help_document_generator.prototype = {
  34     constructor: help_document_generator,
  35     __proto__: dom_generator.prototype,
  36
  37     key_binding: function (str, parent) {
  38         var node = this.element("span", "class", "key-binding");
  39         this.text(str, node);
  40         if (parent)
  41             parent.appendChild(node);
  42         return node;
  43     },
  44
  45     source_code_reference: function (ref, parent) {
  46         var f = this.document.createDocumentFragment();
  47         var module_name = ref.module_name;
  48         var buffer = this.buffer;
  49         //f.appendChild(this.text(module_name != null ? "module " : "file "));
  50         var x = this.element("a",
  51                              "class", "source-code-reference",
  52                              "href", "javascript:");
  53         x.addEventListener("click", function (event) {
  54             spawn(function () {
  55                 try {
  56                     yield ref.open_in_editor();
  57                 } catch (e) {
  58                     handle_interactive_error(buffer.window, e);
  59                 }}());
  60             event.preventDefault();
  61             event.stopPropagation();
  62         }, false /* capture */);
  63         x.textContent = (module_name != null ? module_name : ref.file_name);
  64         f.appendChild(x);
  65         if (parent)
  66             parent.appendChild(f);
  67         return f;
  68     },
  69
  70     command_name: function (name, parent) {
  71         var node = this.element("span", "class", "command");
  72         this.text(name, node);
  73         if (parent)
  74             parent.appendChild(node);
  75         return node;
  76     },
  77
  78     command_reference: function (name, parent) {
  79         var node = this.element("a",
  80                                 "class", "command",
  81                                 "href", "javascript:");
  82         var buffer = this.buffer;
  83         node.addEventListener("click", function (event) {
  84                                   /* FIXME: don't hardcode browse target */
  85                                   describe_command(buffer, name, OPEN_NEW_BUFFER);
  86                                   event.preventDefault();
  87                                   event.stopPropagation();
  88             }, false /* capture */);
  89         this.text(name, node);
  90         if (parent)
  91             parent.appendChild(node);
  92         return node;
  93     },
  94
  95     variable_reference: function (name, parent) {
  96         var node = this.element("a", "class", "variable", "href", "#");
  97         /* FIXME: make this work */
  98         this.text(name, node);
  99         if (parent)
 100             parent.appendChild(node);
 101         return node;
 102     },
 103
 104     help_text: function (str, parent) {
 105         var paras = str.split("\n");
 106         var f = this.document.createDocumentFragment();
 107         for (var i = 0; i < paras.length; ++i) {
 108             var para = paras[i];
 109             if (para.length == 0)
 110                 continue;
 111
 112             var p = this.element("p", f);
 113
 114             var regexp = /`([a-zA-Z0-9_\-$]+)\'/g;
 115
 116             var match;
 117             var last_index = 0;
 118             while ((match = regexp.exec(para)) != null) {
 119                 this.text(para.substring(last_index, match.index), p);
 120                 var command = match[1];
 121                 /* FIXME: check if it is a valid command */
 122                 this.command_reference(command, p);
 123                 last_index = regexp.lastIndex;
 124             }
 125             if (last_index < para.length)
 126                 this.text(para.substring(last_index), p);
 127         }
 128         if (parent != null)
 129             parent.appendChild(f);
 130         return f;
 131     },
 132
 133     add_help_stylesheet: function () {
 134         this.add_stylesheet("chrome://conkeror-gui/content/help.css");
 135     }
 136 };
 137
 138
 139 function help_buffer_modality (buffer, element) {
 140     buffer.keymaps.push(help_buffer_keymap);
 141 }
 142
 143 /*
 144  * Describe Bindings
 145  */
 146
 147 define_keywords("$binding_list");
 148 function describe_bindings_buffer (window) {
 149     this.constructor_begin();
 150     keywords(arguments);
 151     special_buffer.call(this, window, forward_keywords(arguments));
 152     this.binding_list = arguments.$binding_list;
 153     this.modalities.push(help_buffer_modality);
 154     this.constructor_end();
 155 }
 156 describe_bindings_buffer.prototype = {
 157     constructor: describe_bindings_buffer,
 158     toString: function () "#<describe_bindings_buffer>",
 159
 160     title: "Key bindings",
 161
 162     description: "*bindings*",
 163
 164     generate: function () {
 165         var d = this.document;
 166         var list = this.binding_list;
 167         delete this.binding_list;
 168
 169         var list_by_keymap = {};
 170         var keymap_list = [];
 171         for each (let x in list) {
 172             let name = x.bound_in || "";
 173             let km;
 174             if (name in list_by_keymap)
 175                 km = list_by_keymap[name];
 176             else {
 177                 km = list_by_keymap[name] = {list_by_category: {}, category_list: [], name: name};
 178                 keymap_list.push(km);
 179             }
 180             let catname = x.category || "";
 181             let cat;
 182             if (catname in km.list_by_category)
 183                 cat = km.list_by_category[catname];
 184             else {
 185                 cat = km.list_by_category[catname] = [];
 186                 cat.name = catname;
 187                 if (catname == "")
 188                     km.category_list.unshift(cat);
 189                 else
 190                     km.category_list.push(cat);
 191             }
 192             cat.push(x);
 193         }
 194
 195         var g = new help_document_generator(d, this);
 196         g.add_help_stylesheet();
 197
 198         d.body.setAttribute("class", "help-list");
 199
 200         for each (let km in keymap_list) {
 201             g.text(km.name, g.element("h1", d.body));
 202             for each (let cat in km.category_list) {
 203                 if (cat.name != "")
 204                     g.text(cat.name, g.element("h2", d.body));
 205
 206                 let table = g.element("table", d.body);
 207                 for (var i = 0; i < cat.length; ++i) {
 208                     let bind = cat[i];
 209                     let tr = g.element("tr", table, "class", (i % 2 == 0) ? "even" : "odd");
 210                     let seq_td = g.element("td", tr, "class", "key-binding");
 211                     g.text(bind.seq, seq_td);
 212                     let command_td = g.element("td", tr, "class", "command");
 213                     let help_str = null;
 214                     if (bind.command != null) {
 215                         if (typeof(bind.command) == "function") {
 216                             g.text("[function]", command_td);
 217                         } else {
 218                             let cmd = interactive_commands[bind.command];
 219                             if (cmd != null) {
 220                                 g.command_reference(cmd.name, command_td);
 221                                 help_str = cmd.shortdoc;
 222                             } else {
 223                                 g.text(bind.command, command_td);
 224                             }
 225                         }
 226                     } else if (bind.keymap != null) {
 227                         g.text("["+bind.keymap+"]", command_td);
 228                     } else if (bind.fallthrough)
 229                         g.text("[pass through]", command_td);
 230                     let help_td = g.element("td", tr, "class", "help");
 231                     g.text(help_str || "", help_td);
 232                 }
 233             }
 234         }
 235     },
 236
 237     __proto__: special_buffer.prototype
 238 };
 239
 240
 241 function describe_bindings (buffer, target, keymaps, prefix) {
 242     var list = [];
 243     if (! keymaps)
 244         keymaps = get_current_keymaps(buffer.window);
 245     if (prefix)
 246         prefix = format_binding_sequence(
 247             prefix.map(function (x) { return {key:x}; }))+" ";
 248     else
 249         prefix = "";
 250     for_each_key_binding(keymaps, function (binding_stack) {
 251             var last = binding_stack[binding_stack.length - 1];
 252             //we don't care about auto-generated keymap bindings.
 253             if (last.keymap && last.keymap.anonymous)
 254                 return;
 255             let bound_in = null;
 256         outer:
 257             for (let i = binding_stack.length - 1; i >= 0; --i) {
 258                 bound_in = binding_stack[i].bound_in;
 259                 while (bound_in) {
 260                     if (bound_in.name && !bound_in.anonymous)
 261                         break outer;
 262                     bound_in = bound_in.bound_in;
 263                 }
 264             }
 265             var keymap = null;
 266             if (last.keymap && ! last.keymap.anonymous)
 267                 keymap = last.keymap.name;
 268             var bind = {seq: prefix+format_binding_sequence(binding_stack),
 269                         fallthrough: last.fallthrough,
 270                         command: last.command,
 271                         keymap: keymap,
 272                         bound_in: bound_in.name,
 273                         category: last.category
 274                        };
 275             list.push(bind);
 276         });
 277     create_buffer(buffer.window, buffer_creator(describe_bindings_buffer,
 278                                                 $opener = buffer,
 279                                                 $binding_list = list),
 280                   target);
 281 }
 282 function describe_bindings_new_buffer (I) {
 283     describe_bindings(I.buffer, OPEN_NEW_BUFFER);
 284 }
 285 function describe_bindings_new_window (I) {
 286     describe_bindings(I.buffer, OPEN_NEW_WINDOW);
 287 }
 288 interactive("describe-bindings",
 289     "Show a help buffer describing the bindings in the context keymaps, "+
 290     "meaning the top-level keymaps according to the focus context in the "+
 291     "current buffer.",
 292     alternates(describe_bindings_new_buffer,
 293                describe_bindings_new_window));
 294
 295 function describe_active_bindings_new_buffer (I) {
 296     describe_bindings(I.buffer, OPEN_NEW_BUFFER,
 297                       I.keymaps || get_current_keymaps(I.buffer.window),
 298                       I.key_sequence.slice(0, -1));
 299 }
 300 function describe_active_bindings_new_window (I) {
 301     describe_bindings(I.buffer, OPEN_NEW_WINDOW,
 302                       I.keymaps || get_current_keymaps(I.buffer.window),
 303                       I.key_sequence.slice(0, -1));
 304 }
 305 interactive("describe-active-bindings",
 306     "Show a help buffer describing the bindings in the active keymaps, "+
 307     "meaning the keymaps in the middle of an ongoing key sequence.  This "+
 308     "command is intended to be called via `sequence_help_keymap'.  For "+
 309     "that reason, `describe-active-bindings' does not consume and prefix "+
 310     "commands like `universal-argument', as doing so would lead to "+
 311     "ambiguities with respect to the intent of the user.",
 312     describe_active_bindings_new_buffer);
 313
 314
 315 /*
 316  * Apropos Command
 317  */
 318
 319 define_keywords("$command_list");
 320 function apropos_command_buffer (window) {
 321     this.constructor_begin();
 322     keywords(arguments);
 323     special_buffer.call(this, window, forward_keywords(arguments));
 324     this.command_list = arguments.$command_list;
 325     this.modalities.push(help_buffer_modality);
 326     this.constructor_end();
 327 }
 328 apropos_command_buffer.prototype = {
 329     constructor: apropos_command_buffer,
 330     toString: function () "#<apropos_command_buffer>",
 331
 332     title: "Apropos commands",
 333
 334     description: "*Apropos*",
 335
 336     generate: function () {
 337         var d = this.document;
 338         var list = this.command_list;
 339         delete this.command_list;
 340
 341         var g = new help_document_generator(d, this);
 342         g.add_help_stylesheet();
 343
 344         d.body.setAttribute("class", "help-list");
 345
 346         var table = d.createElementNS(XHTML_NS, "table");
 347         for (var i = 0; i < list.length; ++i) {
 348             var binding = list[i];
 349             var tr = d.createElementNS(XHTML_NS, "tr");
 350             tr.setAttribute("class", (i % 2 == 0) ? "even" : "odd");
 351
 352             var command_td = d.createElementNS(XHTML_NS,"td");
 353             g.command_reference(binding.name, command_td);
 354
 355             var shortdoc = "";
 356             if (binding.cmd.shortdoc != null)
 357                 shortdoc = binding.cmd.shortdoc;
 358             tr.appendChild(command_td);
 359
 360             var shortdoc_td = d.createElementNS(XHTML_NS, "td");
 361             shortdoc_td.setAttribute("class", "help");
 362             shortdoc_td.textContent = shortdoc;
 363             tr.appendChild(shortdoc_td);
 364
 365             table.appendChild(tr);
 366         }
 367         d.body.appendChild(table);
 368     },
 369
 370     __proto__: special_buffer.prototype
 371 };
 372
 373
 374 /* TODO: support regexps/etc. */
 375 function apropos_command (buffer, substring, target) {
 376     var list = [];
 377     for (let [name, cmd] in Iterator(interactive_commands)) {
 378         if (name.indexOf(substring) != -1) {
 379             var binding = {name: name, cmd: cmd};
 380             list.push(binding);
 381         }
 382     }
 383     list.sort(function (a,b) {
 384                   if (a.name < b.name)
 385                       return -1;
 386                   if (a.name > b.name)
 387                       return 1;
 388                   return 0
 389               });
 390     create_buffer(buffer.window, buffer_creator(apropos_command_buffer,
 391                                                 $opener = buffer,
 392                                                 $command_list = list),
 393                   target);
 394 }
 395
 396 function apropos_command_new_buffer (I) {
 397     apropos_command(I.buffer,
 398                     (yield I.minibuffer.read($prompt = "Apropos command:",
 399                                              $history = "apropos")),
 400                     OPEN_NEW_BUFFER);
 401 }
 402 function apropos_command_new_window (I) {
 403     apropos_command(I.buffer,
 404                     (yield I.minibuffer.read($prompt = "Apropos command:",
 405                                              $history = "apropos")),
 406                     OPEN_NEW_WINDOW);
 407 }
 408 interactive("apropos-command", "List commands whose names contain a given substring.",
 409             alternates(apropos_command_new_buffer, apropos_command_new_window));
 410
 411
 412
 413 /*
 414  * Describe Command
 415  */
 416
 417 define_keywords("$command", "$bindings");
 418 function describe_command_buffer (window) {
 419     this.constructor_begin();
 420     keywords(arguments);
 421     special_buffer.call(this, window, forward_keywords(arguments));
 422     this.bindings = arguments.$bindings;
 423     this.command = arguments.$command;
 424     this.cmd = interactive_commands[this.command];
 425     this.source_code_reference = this.cmd.source_code_reference;
 426     this.modalities.push(help_buffer_modality);
 427     this.constructor_end();
 428 }
 429 describe_command_buffer.prototype = {
 430     constructor: describe_command_buffer,
 431     toString: function () "#<describe_command_buffer>",
 432
 433     get title () { return "Command help: " + this.command; },
 434
 435     description: "*help*",
 436
 437     generate: function () {
 438         var d = this.document;
 439
 440         var g = new help_document_generator(d, this);
 441
 442         g.add_help_stylesheet();
 443         d.body.setAttribute("class", "describe-command");
 444
 445         var p;
 446
 447         p = g.element("p", d.body);
 448         g.command_reference(this.command, p);
 449         var cmd = interactive_commands[this.command];
 450         if (cmd.source_code_reference)  {
 451             g.text(" is an interactive command in ", p);
 452             g.source_code_reference(cmd.source_code_reference, p);
 453             g.text(".", p);
 454         } else {
 455             g.text(" is an interactive command.", p);
 456         }
 457
 458         if (this.bindings.length > 0) {
 459             p = g.element("p", d.body);
 460             g.text("It is bound to ", p);
 461             for (var i = 0; i < this.bindings.length; ++i) {
 462                 if (i != 0)
 463                     g.text(", ", p);
 464                 g.key_binding(this.bindings[i], p);
 465             }
 466             g.text(".", p);
 467         }
 468
 469         if (cmd.doc != null)
 470             g.help_text(cmd.doc, d.body);
 471     },
 472
 473     __proto__: special_buffer.prototype
 474 };
 475
 476
 477 function describe_command (buffer, command, target) {
 478     var keymaps = get_current_keymaps(buffer.window);
 479     var bindings = keymap_lookup_command(keymaps, command);
 480     create_buffer(buffer.window,
 481                   buffer_creator(describe_command_buffer,
 482                                  $opener = buffer,
 483                                  $command = command,
 484                                  $bindings = bindings),
 485                   target);
 486 }
 487 function describe_command_new_buffer (I) {
 488     describe_command(I.buffer, (yield I.minibuffer.read_command($prompt = "Describe command:")),
 489                      OPEN_NEW_BUFFER);
 490 }
 491 function describe_command_new_window (I) {
 492     describe_command(I.buffer, (yield I.minibuffer.read_command($prompt = "Describe command:")),
 493                      OPEN_NEW_WINDOW);
 494 }
 495 interactive("describe-command", null,
 496             alternates(describe_command_new_buffer, describe_command_new_window));
 497
 498
 499
 500 function view_referenced_source_code (buffer) {
 501     if (buffer.source_code_reference == null)
 502         throw interactive_error("Command not valid in current buffer.");
 503     yield buffer.source_code_reference.open_in_editor();
 504 }
 505 interactive("view-referenced-source-code", null,
 506             function (I) {yield view_referenced_source_code(I.buffer);});
 507
 508
 509 /*
 510  * Describe Key
 511  */
 512
 513 define_keywords("$binding", "$other_bindings", "$key_sequence");
 514 function describe_key_buffer (window) {
 515     this.constructor_begin();
 516     keywords(arguments);
 517     special_buffer.call(this, window, forward_keywords(arguments));
 518     this.key_sequence = arguments.$key_sequence;
 519     this.bindings = arguments.$other_bindings;
 520     this.bind = arguments.$binding;
 521     this.source_code_reference = this.bind.source_code_reference;
 522     this.modalities.push(help_buffer_modality);
 523     this.constructor_end();
 524 }
 525 describe_key_buffer.prototype = {
 526     constructor: describe_key_buffer,
 527     toString: function () "#<describe_key_buffer>",
 528
 529     get title () { return "Key help: " + this.key_sequence; },
 530
 531     description: "*help*",
 532
 533     generate: function () {
 534         var d = this.document;
 535
 536         var g = new help_document_generator(d, this);
 537
 538         g.add_help_stylesheet();
 539         d.body.setAttribute("class", "describe-key");
 540
 541         var p;
 542
 543         p = g.element("p", d.body);
 544         g.key_binding(this.key_sequence, p);
 545         g.text(" is bound to the command ", p);
 546         var command = this.bind.command;
 547         if (command == null)
 548             g.command_name("[pass through]", p);
 549         else
 550             g.command_reference(command, p);
 551         if (this.bind.browser_object != null) {
 552             g.text(" with the browser object, ", p);
 553             if (this.bind.browser_object instanceof Function) {
 554                 g.text("<anonymous browser-object function>", p);
 555             } else if (this.bind.browser_object instanceof browser_object_class) {
 556                 g.text(this.bind.browser_object.name, p);
 557             } else if (typeof(this.bind.browser_object) == "string") {
 558                 g.text('"'+this.bind.browser_object+'"', p);
 559             } else {
 560                 g.text(this.bind.browser_object, p);
 561             }
 562         }
 563         if (this.source_code_reference) {
 564             g.text(" in ", p);
 565             g.source_code_reference(this.source_code_reference, p);
 566         }
 567         g.text(".", p);
 568
 569         if (command != null) {
 570             p = g.element("p", d.body);
 571             g.command_reference(command, p);
 572             var cmd = interactive_commands[command];
 573             if (cmd.source_code_reference)  {
 574                 g.text(" is an interactive command in ", p);
 575                 g.source_code_reference(cmd.source_code_reference, p);
 576                 g.text(".", p);
 577             } else {
 578                 g.text(" is an interactive command.", p);
 579             }
 580
 581             if (this.bindings.length > 0) {
 582                 p = g.element("p", d.body);
 583                 g.text("It is bound to ", p);
 584                 for (var i = 0; i < this.bindings.length; ++i) {
 585                     if (i != 0)
 586                         g.text(", ", p);
 587                     g.key_binding(this.bindings[i], p);
 588                 }
 589                 g.text(".", p);
 590             }
 591
 592             if (cmd.doc != null)
 593                 g.help_text(cmd.doc, d.body);
 594         }
 595     },
 596
 597     __proto__: special_buffer.prototype
 598 };
 599
 600
 601 function describe_key (buffer, key_info, target) {
 602     var bindings;
 603     var seq = key_info[0];
 604     var bind = key_info[1];
 605     var keymaps = get_current_keymaps(buffer.window);
 606     if (bind.command)
 607         bindings = keymap_lookup_command(keymaps, bind.command);
 608     else
 609         bindings = [];
 610     create_buffer(buffer.window,
 611                   buffer_creator(describe_key_buffer,
 612                                  $opener = buffer,
 613                                  $key_sequence = seq.join(" "),
 614                                  $other_bindings = bindings,
 615                                  $binding = bind),
 616                   target);
 617 }
 618 function describe_key_new_buffer (I) {
 619     describe_key(I.buffer,
 620                  (yield I.minibuffer.read_key_binding($prompt = "Describe key:")),
 621                  OPEN_NEW_BUFFER);
 622 }
 623 function describe_key_new_window (I) {
 624     describe_key(I.buffer,
 625                  (yield I.minibuffer.read_key_binding($prompt = "Describe key:")),
 626                  OPEN_NEW_WINDOW);
 627 }
 628
 629 function describe_key_briefly (buffer, key_info) {
 630     var bindings;
 631     var seq = key_info[0];
 632     var bind = key_info[1];
 633     var browser_object = "";
 634     if (bind.browser_object != null) {
 635         browser_object += " on the browser object, ";
 636         if (bind.browser_object instanceof Function) {
 637             browser_object += "<anonymous browser-object function>";
 638         } else if (bind.browser_object instanceof browser_object_class) {
 639             browser_object += bind.browser_object.name;
 640         } else if (typeof(bind.browser_object) == "string") {
 641             browser_object += '"'+bind.browser_object+'"';
 642         } else {
 643             browser_object += bind.browser_object;
 644         }
 645     }
 646     buffer.window.minibuffer.message(seq.join(" ") + " runs the command " + bind.command + browser_object);
 647 }
 648
 649 interactive("describe-key", null,
 650             alternates(describe_key_new_buffer, describe_key_new_window));
 651
 652 interactive("describe-key-briefly", null,
 653     function (I) {
 654         describe_key_briefly(
 655             I.buffer,
 656             (yield I.minibuffer.read_key_binding($prompt = "Describe key:")));
 657     });
 658
 659
 660
 661 /*
 662  * Describe Variable
 663  */
 664
 665 define_keywords("$variable");
 666 function describe_variable_buffer (window) {
 667     this.constructor_begin();
 668     keywords(arguments);
 669     special_buffer.call(this, window, forward_keywords(arguments));
 670     this.variable = arguments.$variable;
 671     this.cmd = user_variables[this.variable];
 672     this.source_code_reference = this.cmd.source_code_reference;
 673     this.modalities.push(help_buffer_modality);
 674     this.constructor_end();
 675 }
 676 describe_variable_buffer.prototype = {
 677     constructor: describe_variable_buffer,
 678     toString: function () "#<describe_variable_buffer>",
 679
 680     get title () { return "Variable help: " + this.variable; },
 681
 682     description: "*help*",
 683
 684     generate: function () {
 685         var d = this.document;
 686
 687         var g = new help_document_generator(d, this);
 688
 689         g.add_help_stylesheet();
 690         d.body.setAttribute("class", "describe-variable");
 691
 692         var p;
 693
 694         p = g.element("p", d.body);
 695         g.variable_reference(this.variable, p);
 696         var uvar = user_variables[this.variable];
 697         if (uvar.source_code_reference)  {
 698             g.text(" is a user variable in ", p);
 699             g.source_code_reference(uvar.source_code_reference, p);
 700             g.text(".", p);
 701         } else {
 702             g.text(" is a user variable.", p);
 703         }
 704
 705         p = g.element("p", d.body);
 706         g.text("Its value is: ", p);
 707         let value = conkeror[this.variable];
 708         {
 709             let s = pretty_print_value(value);
 710             let pre = g.element("pre", p);
 711             g.text(s, pre);
 712         }
 713
 714         if (uvar.doc != null)
 715             g.help_text(uvar.doc, d.body);
 716
 717         if (uvar.default_value !== undefined &&
 718             (uvar.default_value !== value ||
 719              (typeof(uvar.default_value) != "object")))  {
 720             p = g.element("p", d.body);
 721             g.text("Its default value is: ", p);
 722             {
 723                 let s = pretty_print_value(uvar.default_value);
 724                 let pre = g.element("pre", p);
 725                 g.text(s, pre);
 726             }
 727         }
 728     },
 729
 730     __proto__: special_buffer.prototype
 731 };
 732
 733
 734 function describe_variable (buffer, variable, target) {
 735     create_buffer(buffer.window,
 736                   buffer_creator(describe_variable_buffer,
 737                                  $opener = buffer,
 738                                  $variable = variable),
 739                   target);
 740 }
 741 function describe_variable_new_buffer (I) {
 742     describe_variable(I.buffer,
 743                       (yield I.minibuffer.read_user_variable($prompt = "Describe variable:")),
 744                       OPEN_NEW_BUFFER);
 745 }
 746 function describe_variable_new_window (I) {
 747     describe_variable(I.buffer,
 748                       (yield I.minibuffer.read_user_variable($prompt = "Describe variable:")),
 749                       OPEN_NEW_WINDOW);
 750 }
 751 interactive("describe-variable", null,
 752             alternates(describe_variable_new_buffer, describe_variable_new_window));
 753
 754
 755
 756 /*
 757  * Describe Preference
 758  */
 759
 760 function describe_preference (buffer, preference, target) {
 761     let key = preference.charAt(0).toUpperCase() + preference.substring(1);
 762     let url = "http://kb.mozillazine.org/" + key;
 763     browser_object_follow(buffer, target, url);
 764 }
 765 function describe_preference_new_buffer (I) {
 766     describe_preference(I.buffer, (yield I.minibuffer.read_preference($prompt = "Describe preference:")),
 767                         OPEN_NEW_BUFFER);
 768 }
 769 function describe_preference_new_window (I) {
 770     describe_preference(I.buffer, (yield I.minibuffer.read_preference($prompt = "Describe preference:")),
 771                         OPEN_NEW_WINDOW);
 772 }
 773 interactive("describe-preference", null,
 774             alternates(describe_preference_new_buffer, describe_preference_new_window));
 775
 776 provide("help");