$.support's English comments are described in detail here, just a little bit of writing down
Query.support = (function () {var support,all,a,select,opt,input,fragment,tds,events,eventname,i,issupported,div = Document.createelement ("div"), documentelement = document.documentelement;//preliminary Testsdiv.setAttribute (" ClassName "," T ");d iv.innerhtml ="
Aall = Div.getelementsbytagname ("*"); a = Div.getelementsbytagname ("a") [0];//can ' t get basic test support//cannot support the most basic Supports an object that returns support as NULL if (!all | |!all.length | |!a) {return {};} First batch of supports Testsselect = Document.createelement ("select"); opt = Select.appendchild (document.createeleme NT ("option")); input = Div.getelementsbytagname ("input") [0];support = {//IE strips leading whitespace when. InnerHTML is used IE with space use//This code, first create a Div, then use InnerHTML to assign a value to div,//And then check whether the first child element of the Div NodeType is 3 (for text),//is the blank character is insured remain, otherwise not retained. Leadingwhitespace: (Div.firstChild.nodeType = = = 3),//Ensure that tbody is not automatically inserted, in IE tbody is automatically inserted//make sure that tbody elements a ren ' t automatically inserted//IE would insert them into empty tablestbody:!div.getelementsbytagname ("Tbody"). length,// Make sure link is serialized//makes sure that link elements get serialized correctly by innerhtml//This requires a wrapper element in IE on I E requires a contained element htmlserialize:!! Div.getelementsbytagname ("link"). length,//Get TheStyle information from getattribute get information through getattribute//(ie uses. csstext instead) IE uses csstext instead of Style:/top/.test (a.get Attribute ("style")),//Make sure this URLs aren ' t manipulated//(IE normalizes it by default) hrefnormalized: (A.getattri Bute ("href") = = = = "/A"),/Make sure that element opacity exists//(IE uses filter instead)//use a regex to work around a WebKit issue. See #5145opacity:/^0.55/.test (a.style.opacity),//Verify style float existence//(IE uses stylefloat instead of Cssfloa T) Cssfloat:!! a.style.cssfloat,//Make sure so if no value is specified for a checkbox//the IT defaults to "on".//(WebKit defaults To "" instead) Checkon: (Input.value = = = "on"),/Make sure that a selected-by-default option have a working selected prop erty.//(WebKit defaults to False instead of true, IE too, if it's in an optgroup) optselected:opt.selected,//Test Setatt Ribute on CamelCase class. If It works, we need attrfixes when doing Get/setattribute (IE6/7) GetSetAttribute:div.clasSName!== "T",//Tests for enctype support on a form (#6743) Enctype:!! Document.createelement ("form"). enctype,//makes sure cloning an HTML5 element does not cause problems//Where outerhtml is Undefined, this still workshtml5Clone:document.createElement ("Nav"). CloneNode (True). outerHTML!== "<:nav>
",//would be defined latersubmitbubbles:true,changebubbles:true,focusinbubbles:false,deleteexpando:true, Nocloneevent:true,inlineblockneedslayout:false,shrinkwrapblocks:false,reliablemarginright:true,pixelmargin: true};//Jquery.boxmodel DEPRECATED in 1.3, use jQuery.support.boxModel Insteadjquery.boxmodel = Support.boxmodel = (docu Ment.compatmode = = = "Css1compat");/make sure checked status is properly clonedinput.checked = True;support.noclonecheck ed = Input.clonenode (True). checked;//Make sure the options inside disabled selects aren ' t marked as disabled//(We Bkit marks them as disabled) select.disabled = true;support.optdisabled =!opt.disabled;//Test to see if it's possible to Delete an expando from a element//fails in Internet explorertry {delete div.test;} catch (e) {Support.deleteexpando = f Alse;} if (!div.addeventlistener && div.attachevent && div.fireevent) {div.attachevent ("onclick", function () {//Cloning a node shouldn ' t copy over any//Bound event handlers (IE does this) support.nocloneevent = false;}); Div.clonenode (True). FireEvent ("onclick");} Check If a radio maintains its value//after being appended to the Dominput = document.createelement ("input"); Input.val UE = "T"; Input.setattribute ("type", "Radio"), Support.radiovalue = Input.value = = = "T"; Input.setattribute ("Checked", " Checked "),//#11217-webkit loses check when the name was after the checked Attributeinput.setattribute (" name "," T ");d IV . appendchild (input); fragment = Document.createdocumentfragment (); Fragment.appendchild (div.lastchild);//WebKit Doesn ' t clone checked state correctly in Fragmentssupport.checkclone = Fragment.clonenode (True). CloneNode (True). Lastch ild.checked;//Check If a disconnected checkbox would retain its checked//value of true after appended to the DOM (IE6/7) s upport.appendchecked = Input.checked;fragment.removechild (input); Fragment.appendchild (div);//technique from Juriy zaytsev//HTTP://PERFECTIONKILLS.COM/DETECTING-Event-support-without-browser-sniffing///We only care about the case where non-standard event systems//is used, namely I N IE. short-circuiting here helps us to//avoid a eval call (in SetAttribute) which can cause csp//to go haywire. see:https://developer.mozilla.org/en/security/csp//The function of this code is to test the bubbling support of IE//$.support[' changebubbles ']if ( Div.attachevent) {for (I-in {submit:1,change:1,focusin:1}) {eventName = ' on ' + i;issupported = (eventName in div); I F (!issupported) {Div.setattribute (EventName, "return;"); issupported = (typeof div[EventName] = = = "function");} support[i + "Bubbles"] = issupported;}} Fragment.removechild (div);//Null elements to avoid leaks in iefragment = select = Opt = div = input = null;//Run tests That need a body at Doc Readyjquery (function () {var container, outer, inner, table, TD, Offsetsupport,margindiv, Conmargi NTOP, style, HTML, positiontopleftwidthheight,paddingmarginbordervisibility, Paddingmarginborder,body = Document.getelementsbytagnaMe ("Body") [0];if (!body) {//Return for frameset docs, that don ' t has a bodyreturn;} Conmargintop = 1;paddingmarginborder = "Padding:0;margin:0;border:";p ositiontopleftwidthheight = "Position:absolute; top:0;left:0;width:1px;height:1px; "; paddingmarginbordervisibility = Paddingmarginborder + "0;visibility:hidden;"; style = "style=" + positiontopleftwidthheight + paddingmarginborder + "5px solid #000;"; HTML = "" + "
"; container = document.createelement (" div "); container.style.cssText = paddingmarginbordervisibility +" width:0; Height:0;position:static;top:0;margin-top: "+ conmargintop +" px "; Body.insertbefore (container, body.firstchild);// Construct the test elementdiv = document.createelement ("div"); Container.appendchild (div);//Check If table cells still h Ave Offsetwidth/height when they is set//to Display:none and there is still other visible table cells in a//table row; If so, offsetwidth/height is not reliable for use when//determining if a element has been hidden directly using//disp Lay:none (It is still safe to use offsets if a parent element is//hidden; Don safety goggles and see bug #4512 for more I nformation).//(only IE 8 fails this test) div.innerhtml = "
"TDS = Div.getelementsbytagname (" TD "); issupported = (tds[0].offsetheight = = = 0); tds[0].style.display =" "; tds[1 ].style.display = "none";//Check if empty table cells still has offsetwidth/height//(IE <= 8 fail this test) support. Reliablehiddenoffsets = issupported && (tds[0].offsetheight = = = 0);//Check if div with explicit width and no Margin-right incorrectly//gets computed margin-right based on width of container. For more//info See bugs #3333//Fails in WebKit before Feb nightlies//WebKit bug 13343-getcomputedstyle returns WR Ong value for Margin-rightif (window.getcomputedstyle) {div.innerhtml = ""; margindiv = document.createelement ("div"); m ArginDiv.style.width = "0"; marginDiv.style.marginRight = "0";d iv.style.width = "2px";d iv.appendchild (Margindiv); Support.reliablemarginright = (parseint ((window.getComputedStyle (margindiv, null) | | {marginright:0}). MarginRight, 10) | | 0) = = = 0;} if (typeof div.style.zoom!== "undefined") {//ChEck If natively block-level elements act like inline-block//elements when setting their display to ' inline ' and giving// them layout//(IE < 8 does this) div.innerhtml = "";d iv.style.width = div.style.padding = "1px";d Iv.style.border = 0;div . Style.overflow = "hidden";d iv.style.display = "inline";d iv.style.zoom = 1;support.inlineblockneedslayout = ( Div.offsetwidth = = = 3);//Check if elements with layout shrink-wrap their children//(IE 6 does this) Div.style.display = "Block";d iv.style.overflow = "visible";d iv.innerhtml = ""; support.shrinkwrapblocks = (div.offsetwidth!== 3);} Div.style.cssText = positiontopleftwidthheight + paddingmarginbordervisibility;div.innerhtml = Html;outer = Div.firstchild;inner = OUTER.FIRSTCHILD;TD = Outer.nextsibling.firstchild.firstchild;offsetsupport = { Doesnotaddborder: (inner.offsettop!== 5), Doesaddborderfortableandcells: (td.offsettop = = 5)};inner.style.position = "fixed"; inner.style.top = "20px";//Safari Subtracts parent border width here whIch is 5pxoffsetsupport.fixedposition = (Inner.offsettop = = = | | inner.offsettop = = =); inner.style.position = inner. Style.top = ""; outer.style.overflow = "hidden"; outer.style.position = "relative"; o Ffsetsupport.subtractsborderforoverflownotvisible = (Inner.offsettop = = =-5); O Ffsetsupport.doesnotincludemargininbodyoffset = (body.offsettop!== conmargintop), if (window.getComputedStyle) { Div.style.marginTop = "1%"; support.pixelmargin = (window.getComputedStyle (div, null) | | {margintop:0}). margintop!== "1%";} if (typeof container.style.zoom!== "undefined") {container.style.zoom = 1;} Body.removechild (container); margindiv = div = container = null;jquery.extend (support, Offsetsupport);}); return support;}) ();
jquery1.7.2 Source Code Analysis (v) $.support
