Ninjas do Front

E os segredos da trindade

Como um browser funciona?

GET /tour HTTP/1.1
Host: stackoverflow.com
Connection: keep-alive
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/37.0.2062.124 Safari/537.36
Accept-Encoding: gzip,deflate,sdch
Accept-Language: pt-BR,pt;q=0.8,en-US;q=0.6,en;q=0.4,en-GB;q=0.2

Cliente

Servidor

Requisição HTTP

HTTP/1.1 200 OK
Cache-Control: private
Content-Type: text/html; charset=utf-8
Content-Encoding: gzip
Vary: Accept-Encoding
X-Frame-Options: SAMEORIGIN
Set-Cookie: prov=1d60e3f5-1681-45af-b8c8-6a4c117a9462; domain=.stackoverflow.com; expires=Fri, 01-Jan-2055 00:00:00 GMT; path=/; HttpOnly
Date: Mon, 06 Oct 2014 05:18:30 GMT
Content-Length: 11133

<!DOCTYPE html>
<html>
<head>
    
    <title>Tour - Stack Overflow</title>
    <link rel="shortcut icon" href="//cdn.sstatic.net/stackoverflow/img/favicon.ico?v=038622610830">
    <link rel="apple-touch-icon image_src" href="//cdn.sstatic.net/stackoverflow/img/apple-touch-icon.png?v=fd7230a85918">
    <link rel="search" type="application/opensearchdescription+xml" title="Stack Overflow" href="/opensearch.xml">
    <meta name="twitter:card" content="summary">
    <meta name="twitter:domain" content="stackoverflow.com"/>
    <meta property="og:type" content="website" />
    <meta property="og:image" itemprop="image primaryImageOfPage" content="http://cdn.sstatic.net/stackoverflow/img/apple-touch-icon@2.png?v=fde65a5a78c6" />
    <meta name="twitter:title" property="og:title" itemprop="title name" content="Tour" />
    <meta name="twitter:description" property="og:description" itemprop="description" content="Q&A for professional and enthusiast programmers" />
    <meta property="og:url" content="http://stackoverflow.com/tour"/>

    
    
    <script src="//ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script>
    <script src="//cdn.sstatic.net/Js/stub.en.js?v=4eaa44c258f8"></script>
    <link rel="stylesheet" type="text/css" href="//cdn.sstatic.net/stackoverflow/all.css?v=3c88ea6de474">
    
    <script src="//cdn.sstatic.net/Js/about.en.js?v=fca97c8a0eab"></script>

    <script>
        StackExchange.ready(function () {
            StackExchange.about.init('//cdn.sstatic.net');
            StackExchange.using("gps", function () { StackExchange.gps.track("aboutpage.view"); });
        });
    </script>


    <script>
        StackExchange.init({"locale":"en","stackAuthUrl":"https://stackauth.com","serverTime":1412572710,"networkMetaHostname":"meta.stackexchange.com","routeName":"Home/Tour","styleCode":true,"enableUserHovercards":true,"snippets":{"enabled":true,"domain":"stacksnippets.net"},"site":{"name":"Stack Overflow","description":"Q&A for professional and enthusiast programmers","isNoticesTabEnabled":true,"recaptchaPublicKey":"6LdchgIAAAAAAJwGpIzRQSOFaO0pU6s44Xt8aTwc","recaptchaAudioLang":"en","enableNewTagCreationWarning":true,"nonAsciiTags":true,"enableSocialMediaInSharePopup":true,"useGoogleOAuth2":true},"user":{"fkey":"3ff1ae6bd26dfb0e98e872581a496455","isAnonymous":true,"ab":{"homepage_recommended_algo":{"v":"a","g":2}}}});
        StackExchange.using.setCacheBreakers({"js/prettify-full.en.js":"f175cb3ef9f0","js/moderator.en.js":"eacc3f340c48","js/full-anon.en.js":"d3566048b957","js/full.en.js":"0ea01f246aa5","js/wmd.en.js":"4c26fabcc081","js/third-party/jquery.autocomplete.min.js":"e5f01e97f7c3","js/third-party/jquery.autocomplete.min.en.js":"","js/mobile.en.js":"a3258d148a79","js/help.en.js":"637a173e1aa4","js/tageditor.en.js":"01aa013ae6a0","js/tageditornew.en.js":"0014c65f10aa","js/inline-tag-editing.en.js":"7e793ad8611c","js/revisions.en.js":"e707189c34fa","js/review.en.js":"711d2cb34faf","js/tagsuggestions.en.js":"cc108c1afbca","js/post-validation.en.js":"d6f09029c0d1","js/explore-qlist.en.js":"4e6f969d97ee","js/events.en.js":"fe5c1303527e","js/keyboard-shortcuts.en.js":"c9aded39884c","js/external-editor.en.js":"2066101db5f0","js/external-editor.en.js":"2066101db5f0","js/snippet-javascript.en.js":"83fff8554968","js/snippet-javascript-codemirror.en.js":"f9718bd7189f"});
        StackExchange.using("gps", function() {
             StackExchange.gps.init(true);
        });
    </script>
    
        <script>
            StackExchange.ready(function () {
                $('#nav-tour').click(function () {
                    StackExchange.using("gps", function() {
                        StackExchange.gps.track("aboutpage.click", { aboutclick_location: "headermain" }, true);
                    });
                });
            });
        </script>
    
    
</head>
<body class="col1-page about-page new-topbar">
    <noscript><div id="noscript-padding"></div></noscript>
    <div id="notify-container"></div>
    <div id="overlay-header"></div>
    <div id="custom-header"></div>
<div class="topbar">
    <div class="topbar-wrapper">
        
        <div class="js-topbar-dialog-corral">

<div class="topbar-dialog siteSwitcher-dialog dno">
    <div class="header">
        <h3><a href="//stackoverflow.com">current community</a></h3>
    </div>
    <div class="modal-content current-site-container">
        <ul class="current-site">
                <li>
                        <div class="related-links">
            <a href="http://chat.stackoverflow.com" class="js-gps-track"     data-gps-track="site_switcher.click({ item_type:6 })"
>chat</a>
                    <a href="http://blog.stackoverflow.com" class="js-gps-track"     data-gps-track="site_switcher.click({ item_type:7 })"
>blog</a>
            </div>




    <a href="//stackoverflow.com"
       class="current-site-link site-link js-gps-track"
       data-id="1"
       data-gps-track="
        site_switcher.click({ item_type:3 })">
        <div class="site-icon favicon favicon-stackoverflow" title="Stack Overflow"></div>
        Stack Overflow
    </a>

                </li>
                <li class="related-site">
                        <div class="L-shaped-icon-container">
        <span class="L-shaped-icon"></span>
    </div>

                    



    <a href="http://meta.stackoverflow.com"
       class="site-link js-gps-track"
       data-id="552"
       data-gps-track="
            site.switch({ target_site:552, item_type:3 }),
        site_switcher.click({ item_type:4 })">
        <div class="site-icon favicon favicon-stackoverflowmeta" title="Meta Stack Overflow"></div>
        Meta Stack Overflow
    </a>

                </li>
                            <li class="related-site">
                        <div class="L-shaped-icon-container">
        <span class="L-shaped-icon"></span>
    </div>

                    <a class="site-link js-gps-track"
                       href="//careers.stackoverflow.com?utm_source=stackoverflow.com&utm_medium=site-ui&utm_campaign=multicollider"
                            data-gps-track="site_switcher.click({ item_type:9 })"
>
                        <div class="site-icon favicon favicon-careers" title="Stack Overflow Careers"></div>
                        Careers 2.0
                    </a>
                </li>
        </ul>
    </div>
    
    <div class="header" id="your-communities-header">
        <h3>
your communities        </h3>
            
    </div>
    <div class="modal-content" id="your-communities-section">
            
            <div class="call-to-login">
                        <a href="https://stackoverflow.com/users/signup?returnurl=http%3a%2f%2fstackoverflow.com%2ftour" class="js-gps-track"     data-gps-track="site_switcher.click({ item_type:10 })"
>Sign up</a>
                    or
                    <a href="https://stackoverflow.com/users/login?returnurl=http%3a%2f%2fstackoverflow.com%2ftour" class="js-gps-track"     data-gps-track="site_switcher.click({ item_type:11 })"
>log in</a>

                    to customize your list.
            </div>
    </div>
    
    <div class="header">
        <h3><a href="//stackexchange.com/sites">more stack exchange communities</a></h3>
    </div>
    <div class="modal-content">
            <div class="child-content"></div>
    </div>
</div>
        </div>

        <div class="network-items">
            
            <a href="//stackexchange.com" 
               class="topbar-icon icon-site-switcher yes-hover js-site-switcher-button js-gps-track"
               data-gps-track="site_switcher.show"
               title="A list of all 129 Stack Exchange sites">
                <span class="hidden-text">Stack Exchange</span>
            </a>
            
        </div>

        <div class="topbar-links">
            
                <div class="links-container">
                    <span class="topbar-menu-links">
                            <a href="https://stackoverflow.com/users/signup?returnurl=http%3a%2f%2fstackoverflow.com%2ftour" class="login-link">sign up</a>
                            <a href="https://stackoverflow.com/users/login?returnurl=http%3a%2f%2fstackoverflow.com%2ftour" class="login-link">log in</a>
                            <a href="/tour">tour</a>

                            <a href="#" class="icon-help js-help-button" title="Help Center and other resources">
        help
        <span class="triangle"></span>
    </a>
    <div class="topbar-dialog help-dialog js-help-dialog dno">
        <div class="modal-content">
            <ul>
                                    <li>
                        <a href="/tour"     class="js-gps-track" data-gps-track="help_popup.click({ item_type:1 })"
>
                            Tour
                            <span class="item-summary">
                                Start here for a quick overview of the site
                            </span>
                        </a>
                    </li>
                <li>
                    <a href="/help"     class="js-gps-track" data-gps-track="help_popup.click({ item_type:4 })"
>
                        Help Center
                        <span class="item-summary">
                            Detailed answers to any questions you might have
                        </span>
                    </a>
                </li>
                    <li>
                        <a href="//meta.stackoverflow.com"     class="js-gps-track" data-gps-track="help_popup.click({ item_type:2 })"
>
                            Meta
                            <span class="item-summary">
                                Discuss the workings and policies of this site
                            </span>
                        </a>
                    </li>
            </ul>
        </div>
    </div>

                            <a href="//careers.stackoverflow.com">careers 2.0</a>
                    </span>
                </div>

			<div class="search-container">
                <form id="search" action="/search" method="get" autocomplete="off">
                    <input name="q" type="text" placeholder="search" value="" tabindex="1" autocomplete="off" maxlength="240" />
                </form>
			</div>
            	
        </div>      
    </div> 
</div>
<script>
    StackExchange.ready(function () { StackExchange.topbar.init(); });
</script>
    <div class="container">
        <div id="header" class=headeranon>
            <br class="cbt">
            <div id="hlogo">
                <a href="/">
                    Stack Overflow
                </a>
            </div>
            <div id="hmenus">
                <div class="nav mainnavs mainnavsanon">
                    <ul>
                        <li><a id="nav-questions" href="/questions">Questions</a></li>
                        <li><a id="nav-tags" href="/tags">Tags</a></li>
                        <li><a id="nav-users" href="/users">Users</a></li>
                        <li><a id="nav-badges" href="/help/badges">Badges</a></li>
                        <li><a id="nav-unanswered" href="/unanswered">Unanswered</a></li>
                    </ul>
                </div>
                <div class="nav askquestion">
                    <ul>
                        <li>
                            <a id="nav-askquestion"  href="/questions/ask">Ask Question</a>
                        </li>
                    </ul>
                </div>
            </div>
        </div>
        



        <div id="content" class="snippet-hidden">
            






<div id="mainbar-full">
    <div class="content-page new-about-content-page about-content-page">
        <div class="about-intro">
            <h2 class="about-title">Welcome to Stack Overflow</h2>
            <img src="//cdn.sstatic.net/stackoverflow/img/apple-touch-icon.png" class="site-icon" />
            <div class="col-full">
                <p>
                    
<div class="wiki-ph" data-placeholder="WikiPlaceholder-AboutThisSite">
    <div class="wiki-ph-content"><p><strong>Stack Overflow</strong> is a question and answer site for professional and enthusiast programmers. It's built and run <em>by you</em> as part of the <a href="http://stackexchange.com">Stack Exchange</a> network of Q&A sites. With your help, we're working together to build a library of detailed answers to every question about programming.</p>
</div> 


</div>
                </p>

                <p class="helper-text">
                        We're a little bit different from other sites. Here's how:
                </p>
            </div>
        </div>

        <hr />

        <div class="about-qa">
            <h2 class="about-title">
                    Ask questions, get answers, no distractions
            </h2>
            <div class="col-l">
                <p>This site is all about <b>getting answers</b>. It's not a discussion forum. There's no chit-chat.</p>

                <div class="just-qa">
                    <div class="just-questions">
                        <p>Just questions...</p>
                        <div class="arrow-1"></div>
                    </div>
                    <div class="just-answers">
                        <p>...and answers.</p>
                        <div class="arrow-2"></div>
                    </div>
                </div>

                <div class="good-answers">
                    <span class="vote-up-on fl">up vote</span>
                    <p>Good answers are voted up and <b>rise to the top</b>.</p>
                    <p class="helper-text">The best answers show up first so that they are always easy to find.</p>
                </div>

                <div class="accept-answers">
                    <span class="vote-accepted-on fl">accept</span>
                    <p>The person who asked can mark one answer as "accepted".</p>
                    <p class="helper-text">Accepting doesn't mean it's the best answer, it just means that it worked for the person who asked.</p>
                </div>

            </div>

            <div class="col-r shadow">
                <div class="qa-block">
                    <div id="question-header">
    <h1 class="question-hyperlink">Do Swift-based applications work on OS X 10.9/iOS 7 and lower?</h1>
</div>
                        
<div class="about-q">
    <div class="votecell fl">
        <div class="vote">
            <span class="vote-up-off" style="cursor: default;">up vote</span>
            <span class="vote-count-post">14</span>
            <span class="vote-down-off" style="cursor: default;">down vote</span>
                <span class="star-off" style="cursor: default;">favorite</span>
                <div class="favoritecount"><b></b></div>
        </div>
    </div>

    <div class="postcell fr">
        <div class="post-text"><p>Will Swift-based applications work on <a href="http://en.wikipedia.org/wiki/OS_X_Mavericks">OS X 10.9</a> (Mavericks)/iOS 7 and lower?</p>

<p>For example, I have a machine running <a href="http://en.wikipedia.org/wiki/OS_X_Mountain_Lion">OS X 10.8</a> (Mountain Lion), and I am wondering if an application I write in Swift will run on it.</p>
</div> 
                            
        <div class="post-taglist">
            <a href="/questions/tagged/ios" class="post-tag" title="show questions tagged 'ios'" rel="tag">ios</a> <a href="/questions/tagged/osx" class="post-tag" title="show questions tagged 'osx'" rel="tag">osx</a> <a href="/questions/tagged/swift" class="post-tag" title="show questions tagged 'swift'" rel="tag">swift</a> 
        </div>
                    
        <div class="post-signature owner fr">
            <div class="user-info ">
                <div class="user-action-time">
                    asked <span title="2014-06-02 19:25:57Z" class="relativetime">Jun 2 at 19:25</span>
                </div>
                <div class="user-gravatar32">
                    <div class="about-user1">
                        <div class="gravatar-wrapper-32"><img src="http://i.stack.imgur.com/xDQHx.jpg?s=32&g=1" alt="" width="32" height="32"></div>
                    </div>
                </div>
                <div class="user-details">
                    MeIr<br />
                    <span class="reputation-score" title="reputation score " dir="ltr">1,998</span><span title="5 gold badges"><span class="badge1"></span><span class="badgecount">5</span></span><span title="14 silver badges"><span class="badge2"></span><span class="badgecount">14</span></span><span title="38 bronze badges"><span class="badge3"></span><span class="badgecount">38</span></span>
                </div>
            </div>
            </div>
    </div>
</div>

                    <div class="subheader answers-subheader">
                        <h3>2 Answers</h3>
                    </div>

                    <div class="about-a">
    <div class="votecell fl">
        <div class="vote">
            <span class="vote-up-off" style="cursor: default;">up vote</span>
            <span class="vote-count-post">4</span>
            <span class="vote-down-off" style="cursor: default;">down vote</span>
                <span class="vote-accepted-off" style="cursor: default;">accept</span>
        </div>
    </div>

    <div class="postcell fr">
        <div class="post-text">
            <p>Swift code can be deployed to OS X 10.9 and iOS 7.0. It will usually crash at launch on older OS versions.</p>
    
        </div>


        <div class="post-signature fr">
            <div class="user-info ">
                <div class="user-action-time">
                    answered <span title="2014-06-03 08:25:37Z" class="relativetime">Jun 3 at 8:25</span>
                </div>
                <div class="user-gravatar32">
                    <div class="about-user2">
                        <div class="gravatar-wrapper-32"><img src="http://i.stack.imgur.com/haS4F.png?s=32&g=1" alt="" width="32" height="32"></div>
                    </div>
                </div>
                <div class="user-details">
                    Greg Parker<br />
                    <span class="reputation-score" title="reputation score " dir="ltr">3,861</span><span title="5 silver badges"><span class="badge2"></span><span class="badgecount">5</span></span><span title="15 bronze badges"><span class="badge3"></span><span class="badgecount">15</span></span>
                </div>
            </div>
        </div>

    </div>
</div>
                    <div class="about-a">
    <div class="votecell fl">
        <div class="vote">
            <span class="vote-up-off" style="cursor: default;">up vote</span>
            <span class="vote-count-post">3</span>
            <span class="vote-down-off" style="cursor: default;">down vote</span>
        </div>
    </div>

    <div class="postcell fr">
        <div class="post-text">
            <p>Apple has announced that Swift apps will be backward compatible with iOS 7 and OS X Mavericks. The WWDC app is written in Swift.</p>
    
        </div>


        <div class="post-signature fr">
            <div class="user-info ">
                <div class="user-action-time">
                    answered <span title="2014-06-03 00:03:37Z" class="relativetime">Jun 3 at 0:03</span>
                </div>
                <div class="user-gravatar32">
                    <div class="about-user2">
                        <div class="gravatar-wrapper-32"><img src="https://www.gravatar.com/avatar/3d2bec5d4578ac8965bb8610fe890237?s=32&d=identicon&r=PG" alt="" width="32" height="32"></div>
                    </div>
                </div>
                <div class="user-details">
                    Ben Gottlieb<br />
                    <span class="reputation-score" title="reputation score 61060" dir="ltr">61.1k</span><span title="10 gold badges"><span class="badge1"></span><span class="badgecount">10</span></span><span title="142 silver badges"><span class="badge2"></span><span class="badgecount">142</span></span><span title="150 bronze badges"><span class="badge3"></span><span class="badgecount">150</span></span>
                </div>
            </div>
        </div>

    </div>
</div>
                </div>
            </div>
        </div>

        <hr />

        <div class="about-offtopic">
                <h2 class="about-title">Get answers to practical, detailed questions</h2>
            <div class="col-l on-topic-text">
                    <p>Focus on questions about an <b>actual problem</b> you have faced. Include details about what you have tried and exactly what you are trying to do.</p>
                <div class="arrow-4"></div>
            </div>

            <div class="col-r">
                <div class="on-topic-examples content-block">
                    <p>Ask about...</p>

                    
<div class="wiki-ph" data-placeholder="WikiPlaceholder-AboutOnTopic">
    <div class="wiki-ph-content"><ul>
    <li>Specific programming problems</li>
    <li>Software algorithms</li>
    <li>Coding techniques</li>
    <li>Software development tools</li></ul>
</div> 


</div>
                </div>
            </div>

            <div class="col-l off-topic-text">
                    <p>Not all questions work well in our format. Avoid questions that are <b>primarily opinion-based</b>, or that are likely to <b>generate discussion</b> rather than answers.</p>
                    <p class="helper-text">Questions that need improvement may be <b>closed</b> until someone fixes them.</p>
                <div class="arrow-4"></div>
            </div>

            <div class="col-r">
                <div class="off-topic-examples content-block">
                        <p>Don't ask about...</p>

                    
<div class="wiki-ph" data-placeholder="WikiPlaceholder-AboutOffTopic">
    <div class="wiki-ph-content"><ul>
<li>Questions you haven't <em>tried</em> to find an answer for (show your work!)</li>
<li>Product or service recommendations or comparisons</li>
<li>Requests for lists of things, polls, opinions, discussions, etc.</li>
<li>Anything not directly related to writing computer programs</li>
</ul>
</div> 


</div>
                </div>
            </div>
        </div>

        <hr />


        <div class="about-tags">
            <h2 class="about-title">Tags make it easy to find interesting questions</h2>

            <div class="col-l">
                <p>All questions are <b>tagged</b> with their subject areas. Each can have up to 5 tags, since a question might be related to several subjects.</p>
                    <p><b>Click any tag</b> to see a list of questions with that tag, or go to the <a href="/tags">tag list</a> to browse for topics that interest you.</p>
                <div class="arrow-2"></div>
            </div>

            <div class="col-r shadow">
                <div class="qa-block">
                    <div id="question-header">
    <h1 class="question-hyperlink">Do Swift-based applications work on OS X 10.9/iOS 7 and lower?</h1>
</div>
                        
<div class="about-q">
    <div class="votecell fl">
        <div class="vote">
            <span class="vote-up-off" style="cursor: default;">up vote</span>
            <span class="vote-count-post">14</span>
            <span class="vote-down-off" style="cursor: default;">down vote</span>
        </div>
    </div>

    <div class="postcell fr">
        <div class="post-text"><p>Will Swift-based applications work on <a href="http://en.wikipedia.org/wiki/OS_X_Mavericks">OS X 10.9</a> (Mavericks)/iOS 7 and lower?</p>

<p>For example, I have a machine running <a href="http://en.wikipedia.org/wiki/OS_X_Mountain_Lion">OS X 10.8</a> (Mountain Lion), and I am wondering if an application I write in Swift will run on it.</p>
</div> 
                            
        <div class="post-taglist">
            <a href="/questions/tagged/ios" class="post-tag" title="show questions tagged 'ios'" rel="tag">ios</a> <a href="/questions/tagged/osx" class="post-tag" title="show questions tagged 'osx'" rel="tag">osx</a> <a href="/questions/tagged/swift" class="post-tag" title="show questions tagged 'swift'" rel="tag">swift</a> 
        </div>
                    
        <div class="post-signature owner fr">
            <div class="user-info ">
                <div class="user-action-time">
                    asked <span title="2014-06-02 19:25:57Z" class="relativetime">Jun 2 at 19:25</span>
                </div>
                <div class="user-gravatar32">
                    <div class="about-user1">
                        <div class="gravatar-wrapper-32"><img src="http://i.stack.imgur.com/xDQHx.jpg?s=32&g=1" alt="" width="32" height="32"></div>
                    </div>
                </div>
                <div class="user-details">
                    MeIr<br />
                    <span class="reputation-score" title="reputation score " dir="ltr">1,998</span><span title="5 gold badges"><span class="badge1"></span><span class="badgecount">5</span></span><span title="14 silver badges"><span class="badge2"></span><span class="badgecount">14</span></span><span title="38 bronze badges"><span class="badge3"></span><span class="badgecount">38</span></span>
                </div>
            </div>
            </div>
    </div>
</div>
                </div>
            </div>
        </div>

        <hr />
        <div class="about-reputation">
            <h2 class="about-title">You earn reputation when people vote on your posts</h2>

            <div class="about-rep-score col-l">
                <p>Your reputation score goes up when others <b>vote up</b> your questions, answers and edits.</p>
                <div class="arrow-2"></div>
            </div>

            <div class="col-r">
                <div class="all-rep-block">
                    <div class="user-info-rep">
                        <div class="about-gravatar"></div>
                        <div class="user-details">
                            John Doe<br>United States
                            <br />
                            <span class="reputation-score" title="reputation score" dir="ltr">245</span>
                            <span title="3 gold badges"><span class="badge1"></span><span class="badgecount">3</span></span>
                            <span title="22 silver badges"><span class="badge2"></span><span class="badgecount">22</span></span>
                            <span title="74 bronze badges"><span class="badge3"></span><span class="badgecount">74</span></span>
                        </div>
                    </div>

                    <div class="fr">
                        <div class="rep-block fl">
                            <span class="rep-up">+5</span>
                            question voted up
                        </div>
                        <div class="rep-block fl">
                            <span class="rep-up">+10</span>
                            answer voted up
                        </div>
                        <div class="rep-block fl">
                            <span class="rep-up">+15</span>
                            answer is accepted
                        </div>
                        <div class="rep-block fl">
                            <span class="rep-up">+2</span>
                            edit approved
                        </div>
                    </div>
                </div>
            </div>

            <div class="about-rep-privs col-l">
                <p>As you earn reputation, you'll <a href="/help/privileges">unlock new privileges</a> like the ability to vote, comment, and even edit other people's posts.</p>
                <div class="arrow-4"></div>
            </div>

            <div class="col-r">
                <div class="content-block">
                    <table>
                        <thead>
                            <tr>
                                <th>Reputation</th>
                                <th>Privilege</th>
                            </tr>
                        </thead>
                        <tbody>
                                <tr>
                                    <th>15</th>
                                    <td>Vote up</td>
                                </tr>
                                <tr>
                                    <th>50</th>
                                    <td>Leave comments</td>
                                </tr>
                                <tr>
                                    <th>125</th>
                                    <td>Vote down (costs <b>1</b> rep on answers)</td>
                                </tr>
                        </tbody>
                    </table>
                </div>
            </div>

            <div class="about-rep-privs-2 col-l">
                <p>At the highest levels, you'll have access to special <b>moderation tools</b>. You'll be able to work alongside our <a href="/users?tab=moderators">community moderators</a> to keep the site focused and helpful.</p>
                <div class="arrow-4"></div>
            </div>
            <div class="col-r">
                <div class="content-block">
                    <table>
                        <tbody>
                                <tr>
                                    <th>2000</th>
                                    <td>Edit other people's posts</td>
                                </tr>
                                <tr>
                                    <th>3000</th>
                                    <td>Vote to close, reopen, or migrate questions</td>
                                </tr>
                                <tr>
                                    <th>10000</th>
                                    <td>Access to moderation tools</td>
                                </tr>
                        </tbody>
                    </table>
                    <a href="/help/privileges">see all privileges</a>
                </div>
            </div>
        </div>
        <hr />
        <div class="about-editing">
            <h2 class="about-title">Improve posts by editing or commenting</h2>

            <div class="col-l">
                <div class="editing">
                    <p>Our goal is to have the <b>best answers</b> to every question, so if you see questions or answers that can be improved, you can <b>edit</b> them.</p>
                    <p class="helper-text">Use edits to fix mistakes, improve formatting, or clarify the meaning of a post.</p>
                    <div class="arrow-2"></div>
                </div>

                <div class="commenting">
                    <p>Use <b>comments</b> to ask for more information or clarify a question or answer.</p>

                    <p class="helper-text">You can always comment on <b>your own</b> questions and answers. Once you earn 50 reputation, you can comment on anybody's post.</p>

                    <p>Remember: we're all here to learn, so be friendly and helpful!</p>

                    <div class="arrow-2"></div>
                </div>
            </div>

            <div class="col-r shadow">
                <div class="qa-block qa-answer">
                    <div class="about-a">
    <div class="votecell fl">
        <div class="vote">
            <span class="vote-up-off" style="cursor: default;">up vote</span>
            <span class="vote-count-post">9</span>
            <span class="vote-down-off" style="cursor: default;">down vote</span>
        </div>
    </div>

    <div class="postcell fr">
        <div class="post-text">
            <p>Swift code can be deployed to OS X 10.9 and iOS 7.0. It will usually crash at launch on older OS versions.</p>
    
        </div>

            <p class="post-menu"><a style="cursor: default;">edit</a></p>

        <div class="post-signature fr">
            <div class="user-info ">
                <div class="user-action-time">
                    answered <span title="2014-06-03 08:25:37Z" class="relativetime">Jun 3 at 8:25</span>
                </div>
                <div class="user-gravatar32">
                    <div class="about-user2">
                        <div class="gravatar-wrapper-32"><img src="http://i.stack.imgur.com/haS4F.png?s=32&g=1" alt="" width="32" height="32"></div>
                    </div>
                </div>
                <div class="user-details">
                    Greg Parker<br />
                    <span class="reputation-score" title="reputation score " dir="ltr">3,861</span><span title="5 silver badges"><span class="badge2"></span><span class="badgecount">5</span></span><span title="15 bronze badges"><span class="badge3"></span><span class="badgecount">15</span></span>
                </div>
            </div>
        </div>

            <div class="comments">
                <div class="comment-entry border-red">That's as definitive as it gets. Mr. Parker is in the guts of it. - uchuugaka <span title="2014-06-03 09:27:11Z" class="relativetime">Jun 3 at 9:27</span></div>
            </div>
            <p><a class="comments-link" style="cursor: default;">add comment</a></p>
    </div>
</div>
                </div>
            </div>
        </div>
        <hr />
        <div class="about-badges">

            <h2 class="about-title">Unlock badges for special achievements</h2>

            <div class="col-l">
                <p>Badges are special achievements you earn for participating on the site. They come in three levels: bronze, silver, and gold.</p>

                <div class="informed-badge">
                        <p>In fact, you can earn a badge just for reading this page:</p>

                    <table class="badges-page">
                                            <tr>
                        <td class="badge-cell">
                            <a  href="/help/badges/2600/informed" 
    title="bronze badge: Read the entire tour page"
    class="badge"><span class="badge3"></span> Informed</a>
                        </td>
                        <td>
                            Read the entire <a href="http://stackoverflow.com/tour">tour</a> page
                        </td>
                    </tr>

                    </table>
                </div>
            </div>

            <div class="col-r shadow">
                <div class="qa-block">
                    <table class="badges-page">
                        <tbody>
                                                <tr>
                        <td class="badge-cell">
                            <a  href="/help/badges/2/student" 
    title="bronze badge: Asked first question with score of 1 or more"
    class="badge"><span class="badge3"></span> Student</a>
                        </td>
                        <td>
                            Asked first question with score of 1 or more
                        </td>
                    </tr>

                                                <tr>
                        <td class="badge-cell">
                            <a  href="/help/badges/3/editor" 
    title="bronze badge: First edit"
    class="badge"><span class="badge3"></span> Editor</a>
                        </td>
                        <td>
                            First edit
                        </td>
                    </tr>

                                                <tr>
                        <td class="badge-cell">
                            <a  href="/help/badges/24/good-answer" 
    title="silver badge: Answer score of 25 or more"
    class="badge"><span class="badge2"></span> Good Answer</a>
                        </td>
                        <td>
                            Answer score of 25 or more
                        </td>
                    </tr>

                                                <tr>
                        <td class="badge-cell">
                            <a  href="/help/badges/32/civic-duty" 
    title="silver badge: Voted 300 or more times"
    class="badge"><span class="badge2"></span> Civic Duty</a>
                        </td>
                        <td>
                            Voted 300 or more times
                        </td>
                    </tr>

                                                <tr>
                        <td class="badge-cell">
                            <a  href="/help/badges/28/famous-question" 
    title="gold badge: Asked a question with 10,000 views"
    class="badge"><span class="badge1"></span> Famous Question</a>
                        </td>
                        <td>
                            Asked a question with 10,000 views
                        </td>
                    </tr>

                        </tbody>
                    </table>

                    <p><a href="/help/badges">see all badges</a></p>
                </div>
            </div>
        </div>
        <hr />
        <div class="about-newuser">
            <h2 class="about-title">Find a question to answer, or ask your own</h2>
            <div class="col-full">
                <div id="huge-buttons">
                    <a href="/questions?sort=newest" id="new-questions" class="button huge-button">See new questions</a><a href="/questions/ask" id="ask-your-own" class="button huge-button">Ask a question</a>
                </div>
                <div class="col-full" style="text-align: center; margin-top: 3em;">
                    Looking for more in-depth information on the site? <a href="/help" class="button" id="visit-the-faq" style="margin-left: 2em">Visit the Help Center</a>
                </div>
            </div>
        </div>

        <hr />

        <div class="about-se">
            <div class="col-full">
                <h2 class="about-title">Stack Overflow is part of the Stack Exchange network</h2>
                <p>Like this site? Stack Exchange is a network of 128 Q&A sites just like it. Check out the <a href="http://stackexchange.com/sites" id="full_list_of_sites">full list of sites</a>.
                </p>
                <p><a href="http://stackexchange.com">
                       <img src="https://cdn.sstatic.net/stackexchange/img/apple-touch-icon.png" class="site-icon" alt="Stack Exchange" /></a></p>
            </div>
        </div>
    </div>
</div>

        </div>
    </div>
    <div id="footer" class="categories">
        <div class="footerwrap">
            <div id="footer-menu">
                <div class="top-footer-links">
                        <a href="/tour">tour</a>
                    <a href="/help">help</a>
                        <a href="/help/badges">badges</a>
                    <a href="http://blog.stackoverflow.com?blb=1">blog</a>
                        <a href="http://chat.stackoverflow.com">chat</a>
                    <a href="http://data.stackexchange.com">data</a>
                    <a href="http://stackexchange.com/legal">legal</a>
                    <a href="http://stackexchange.com/legal/privacy-policy">privacy policy</a>
                    <a href="http://stackexchange.com/work-here">work here</a>
                    <a href="http://stackexchange.com/mediakit">advertising info</a>

                    <a onclick='StackExchange.switchMobile("on")'>mobile</a>
                    <b><a href="/contact">contact us</a></b>
                        <b><a href="http://meta.stackoverflow.com">feedback</a></b>
                    
                </div>
                <div id="footer-sites">
                    <table>
    <tr>
            <th colspan=3>
                Technology
            </th>
            <th >
                Life / Arts
            </th>
            <th >
                Culture / Recreation
            </th>
            <th >
                Science
            </th>
            <th >
                Other
            </th>
    </tr>
    <tr>
            <td>
                <ol>
                        <li><a href="//stackoverflow.com" title="professional and enthusiast programmers">Stack Overflow</a></li>
                        <li><a href="//serverfault.com" title="professional system and network administrators">Server Fault</a></li>
                        <li><a href="//superuser.com" title="computer enthusiasts and power users">Super User</a></li>
                        <li><a href="//webapps.stackexchange.com" title="power users of web applications">Web Applications</a></li>
                        <li><a href="//askubuntu.com" title="Ubuntu users and developers">Ask Ubuntu</a></li>
                        <li><a href="//webmasters.stackexchange.com" title="pro webmasters">Webmasters</a></li>
                        <li><a href="//gamedev.stackexchange.com" title="professional and independent game developers">Game Development</a></li>
                        <li><a href="//tex.stackexchange.com" title="users of TeX, LaTeX, ConTeXt, and related typesetting systems">TeX - LaTeX</a></li>
                            </ol></td><td><ol>
                        <li><a href="//programmers.stackexchange.com" title="professional programmers interested in conceptual questions about software development">Programmers</a></li>
                        <li><a href="//unix.stackexchange.com" title="users of Linux, FreeBSD and other Un*x-like operating systems.">Unix & Linux</a></li>
                        <li><a href="//apple.stackexchange.com" title="power users of Apple hardware and software">Ask Different (Apple)</a></li>
                        <li><a href="//wordpress.stackexchange.com" title="WordPress developers and administrators">WordPress Development</a></li>
                        <li><a href="//gis.stackexchange.com" title="cartographers, geographers and GIS professionals">Geographic Information Systems</a></li>
                        <li><a href="//electronics.stackexchange.com" title="electronics and electrical engineering professionals, students, and enthusiasts">Electrical Engineering</a></li>
                        <li><a href="//android.stackexchange.com" title="enthusiasts and power users of the Android operating system">Android Enthusiasts</a></li>
                        <li><a href="//security.stackexchange.com" title="Information security professionals">Information Security</a></li>
                            </ol></td><td><ol>
                        <li><a href="//dba.stackexchange.com" title="database professionals who wish to improve their database skills and learn from others in the community">Database Administrators</a></li>
                        <li><a href="//drupal.stackexchange.com" title="Drupal developers and administrators">Drupal Answers</a></li>
                        <li><a href="//sharepoint.stackexchange.com" title="SharePoint enthusiasts">SharePoint</a></li>
                        <li><a href="//ux.stackexchange.com" title="user experience researchers and experts">User Experience</a></li>
                        <li><a href="//mathematica.stackexchange.com" title="users of Mathematica">Mathematica</a></li>
                        <li><a href="//salesforce.stackexchange.com" title="Salesforce administrators, implementation experts, developers and anybody in-between">Salesforce</a></li>
                    
                        <li>
                            <a href="http://stackexchange.com/sites#technology" class="more">
                                more (13)
                            </a>
                        </li>
                </ol>
            </td>
            <td>
                <ol>
                        <li><a href="//photo.stackexchange.com" title="professional, enthusiast and amateur photographers">Photography</a></li>
                        <li><a href="//scifi.stackexchange.com" title="science fiction and fantasy enthusiasts">Science Fiction & Fantasy</a></li>
                        <li><a href="//graphicdesign.stackexchange.com" title="Graphic Design professionals, students, and enthusiasts">Graphic Design</a></li>
                        <li><a href="//cooking.stackexchange.com" title="professional and amateur chefs">Seasoned Advice (cooking)</a></li>
                        <li><a href="//diy.stackexchange.com" title="contractors and serious DIYers">Home Improvement</a></li>
                        <li><a href="//money.stackexchange.com" title="people who want to be financially literate">Personal Finance & Money</a></li>
                        <li><a href="//academia.stackexchange.com" title="academics and those enrolled in higher education">Academia</a></li>
                    
                        <li>
                            <a href="http://stackexchange.com/sites#lifearts" class="more">
                                more (10)
                            </a>
                        </li>
                </ol>
            </td>
            <td>
                <ol>
                        <li><a href="//english.stackexchange.com" title="linguists, etymologists, and serious English language enthusiasts">English Language & Usage</a></li>
                        <li><a href="//skeptics.stackexchange.com" title="scientific skepticism">Skeptics</a></li>
                        <li><a href="//judaism.stackexchange.com" title="those who base their lives on Jewish law and tradition and anyone interested in learning more">Mi Yodeya (Judaism)</a></li>
                        <li><a href="//travel.stackexchange.com" title="road warriors and seasoned travelers">Travel</a></li>
                        <li><a href="//christianity.stackexchange.com" title="committed Christians, experts in Christianity and those interested in learning more">Christianity</a></li>
                        <li><a href="//gaming.stackexchange.com" title="passionate videogamers on all platforms">Arqade (gaming)</a></li>
                        <li><a href="//bicycles.stackexchange.com" title="people who build and repair bicycles, people who train cycling, or commute on bicycles">Bicycles</a></li>
                        <li><a href="//rpg.stackexchange.com" title="gamemasters and players of tabletop, paper-and-pencil role-playing games">Role-playing Games</a></li>
                    
                        <li>
                            <a href="http://stackexchange.com/sites#culturerecreation" class="more">
                                more (21)
                            </a>
                        </li>
                </ol>
            </td>
            <td>
                <ol>
                        <li><a href="//math.stackexchange.com" title="people studying math at any level and professionals in related fields">Mathematics</a></li>
                        <li><a href="//stats.stackexchange.com" title="people interested in statistics, machine learning, data analysis, data mining, and data visualization">Cross Validated (stats)</a></li>
                        <li><a href="//cstheory.stackexchange.com" title="theoretical computer scientists and researchers in related fields">Theoretical Computer Science</a></li>
                        <li><a href="//physics.stackexchange.com" title="active researchers, academics and students of physics">Physics</a></li>
                        <li><a href="//mathoverflow.net" title="professional mathematicians">MathOverflow</a></li>
                    
                        <li>
                            <a href="http://stackexchange.com/sites#science" class="more">
                                more (7)
                            </a>
                        </li>
                </ol>
            </td>
            <td>
                <ol>
                        <li><a href="//stackapps.com" title="apps, scripts, and development with the Stack Exchange API">Stack Apps</a></li>
                        <li><a href="//meta.stackexchange.com" title="meta-discussion of the Stack Exchange family of Q&A websites">Meta Stack Exchange</a></li>
                        <li><a href="//area51.stackexchange.com" title="proposing new sites in the Stack Exchange network">Area 51</a></li>
                        <li><a href="//careers.stackoverflow.com?utm_source=stackoverflow.com&utm_medium=site-ui&utm_campaign=footerlink">Stack Overflow Careers</a></li>
                    
                </ol>
            </td>
    </tr>
</table>
                </div>
            </div>

            <div id="copyright">
                site design / logo © 2014 stack exchange inc; user contributions licensed under <a href="http://creativecommons.org/licenses/by-sa/3.0/" rel="license">cc by-sa 3.0</a> 
                with <a href="http://blog.stackoverflow.com/2009/06/attribution-required/" rel="license">attribution required</a>
            </div>
            <div id="svnrev">
                rev 2014.10.4.1909
            </div>
            
        </div>
    </div>
    <noscript>
        <div id="noscript-warning">Stack Overflow works best with JavaScript enabled<img src="http://pixel.quantserve.com/pixel/p-c1rF4kxgLUzNc.gif" alt="" class="dno"></div>
    </noscript>

    <script>
        (function (i, s, o, g, r, a, m) {
            i['GoogleAnalyticsObject'] = r; i[r] = i[r] || function () { (i[r].q = i[r].q || []).push(arguments) }, i[r].l = 1 * new Date(); a = s.createElement(o),
            m = s.getElementsByTagName(o)[0]; a.async = 1; a.src = g; m.parentNode.insertBefore(a, m);
        })(window, document, 'script', '//www.google-analytics.com/analytics.js', 'ga');
        ga('create', 'UA-5620270-1');        
        
        
        ga('send', 'pageview');
        var _qevents = _qevents || [],
            _comscore = _comscore || [];
        (function () {
            var ssl='https:'==document.location.protocol,
                s=document.getElementsByTagName('script')[0],
                qc=document.createElement('script');
            qc.async=true;
            qc.src=(ssl?'https://secure':'http://edge')+'.quantserve.com/quant.js';
            s.parentNode.insertBefore(qc, s);
            var sc=document.createElement('script');
            sc.async=true;
            sc.src=(ssl?'https://sb':'http://b') + '.scorecardresearch.com/beacon.js';
            s.parentNode.insertBefore(sc, s);
        })();
        _comscore.push({ c1: "2", c2: "17440561" });
        _qevents.push({ qacct: "p-c1rF4kxgLUzNc" });
    </script>        
    
    </body>
</html>

Como um browser funciona?

HTML e DOM

Linguagem de marcação, apenas texto.

HTML

DOM

Interface de programação para documentos HTML, XML e SVG.

Provê uma representação estruturada do documento, permitindo acessar esta estrutura, assim como alterar a estrutura, estilo e conteúdo do documento.

Como um browser funciona?

HTML e DOM

<!DOCTYPE html>
<html>
    <head>
        <title>My title</title>
    </head>
    <body>
        <a href="">My link</a>
        <h1>My header</h1>
    </body>
</html>

HTML

DOM

Como um browser funciona?

CSS e CSSOM

Cascading Style Sheets (CSS) é uma linguagem de estilo usada para descrever a apresentação de um documento escrito em HTML ou em XML (incluindo várias linguagens em XML como SVG ou XHTML).

CSS

CSSOM

Define APIs (incluindo regras de parsing e serialização genéricas) para Seletores, Media Queries, e é claro, o próprio CSS.

Como um browser funciona?

CSS e CSSOM

Seletor seguido de bloco de declarações.

Rule ou Rule set

Como um browser funciona?

Render Tree

Como um browser funciona?

Render Tree

Como um browser funciona?

JavaScript

  • Linguagem de scripting
  • Orientado a objetos
  • Single thread, orientado a eventos
  • Seu padrão é o ECMAScript

Como um browser funciona?

JavaScript e DOM

DOM expõe APIs para linguagens de programação (notavelmente JavaScript) acessar e manipular tudo dentro do documento, incluindo sua estrutura, estilo e conteúdo.

Como um browser funciona?

Render blocking

  • Nada é renderizado na tela até que todos arquivos CSS estejam carregados.
  • Tag <script> (sem os atributo defer/async) bloqueia a construção do DOM até que a mesma seja carregada e executada.

Como um browser funciona?

HTML (DOM)

CSS (CSSOM)

JavaScript

Fontes

  • http://css.maxdesign.com.au/selectutorial/rule.htm
  • https://developers.google.com/web/fundamentals/performance/critical-rendering-path/render-tree-construction
  • https://developer.mozilla.org/en-US/docs/Web/API/Document_Object_Model
  • https://developer.mozilla.org/pt-BR/docs/Web/CSS
  • http://dev.w3.org/csswg/cssom/
  • http://www.phpied.com/dom-access-optimization/

Ninjas do Front e os Segredos da Trindade #1

By Fabrício Matté

Ninjas do Front e os Segredos da Trindade #1

#SASPI5 minicurso ministrado por @Ult_Combo e @_jotavejv

  • 1,797