HTML5设计原理Word文件下载.docx

HTML5设计原理Word文件下载.docx

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Actually,someotherpeoplearegoingtobetalkingaboutthecontentsofthespec.SteveFaulknerwillbetalkingaboutaccessibilityandHTML5.PaulIrishisgoingtogothroughawholebunchoftheAPIsthatareinHTML5.SoI’mnotjustgoingtostanduphereandrunthroughwhat’sinHTML5.

Actually,beforeIevengetstartedIshouldprobablyclarifywhatImeanbyHTML5,whichseemskindofcrazy‘causewhyshouldIhavetoclarifywhatImeanbyHTML5whenwhatImeanbyHTML5isHTML5?

There’saspecification,it’scalledHTML5andwhenIsayHTML5that’swhatIamreferringto.TheproblemisotherpeopleareusingthetermHTML5torefertojustaboutanything,whichcanbeproblematic.Forexample,referringtoCSS3asHTML5forsomereasonseemstobeacommontechnique.That’snotwhatI’mreferringto.WhenIsayHTML5Idon’tmeanCSS3,ImeanHTML5.

We’vebeenherebeforewithterms.ItusedtobethatAjaxmeantsomethingspecificandthen,afterawhile,itjustbecame“doinganythingcoolwithJavascript.”ThatwasAjax,right?

AndnowthesamethingseemstobehappeningtothetermHTML5.It’ssupposedtomeanaspecificspecificationandnowitjustmeans“doinganythingcool（fullstop）ontheweb.”Butthat’snottheHTML5Imean.Idon’tmeanthisumbrellatermthatcoversanythingthat’snewthesedays.I’mspecificallytalkingaboutthespecification:

HTML5.

AsIsaid,it’snotsomuchthecontentsIwanttotalkabout.It’snotgoingthroughachecklistofwhat’sinHTML5.It’stheothersideofit,it’sthedesignofHTML5.WhatIwanttotalkaboutisnotsomuchwhatisinthespecbutwhythesethingsareinthespec,whattheprocesswasinthinkingofthesethingswhendesigningaspecification.

Inparticular,oneofthereasonswhyIthinkHTML5asaspecificationisquitesuccessful—andtheprocesshasbeensuccessful—isthatitisdrivenbydesignprinciples.DesignprinciplesaresomethingIamgettingmoreandmorefascinatedwith.

Designprinciples

Adesignprincipleisessentiallyabelief,atenant,aconceptthatyourallybehind.Itdoesn’tmatterwetheryourmakingaspecificationorifyouaremakingaphysicalobjectorapieceofsoftwareoraprogramminglanguage.Youwillprobablyfindadesignprincipleormultipledesignprinciplesbehindallgoodexamplesofanythingthathasbeenbuiltcollaboratively.Andit’snotjustfromtheworldoftheweb.Throughouthistorythereexampleofdesignprinciplesbehindlargescaleconstructionslikecountries,societies.

Togiveyouanexample,fromtheUnitedStatesofAmerica,thisisadesignprinciplebuiltintotheDeclarationofIndependence.

WeholdtheseTruthstobeself-evident,thatallMenarecreatedequal,thattheyareendowedbytheirCreatorwithcertainunalienableRights,thatamongtheseareLife,LibertyandthepursuitofHappiness.

Theyhavethewatchwordsinthere:

life,liberty,thepursuitofhappiness.Thesearethekeysthingsenthronedintotheconstitution,thisiswhatweareallabout,thesearetheprinciplesonwhichwewanttobuildoursociety.

AnotherexamplewouldbefromKarlMarxwhosewritingwereusedasabasisforbuildingsocietiesthroughoutthe20thcenturyandalotofitcouldbeboileddowntothisonedesignprinciple:

Fromeachaccordingtohisability,toeachaccordingtohisneed.

Soherewehavethisdesignprincipleguidinganeconomicsystem.

Anotherexample,mucholderthanthatbutusingasimilarprincipletothiswouldbe:

Dountoothersasyouwouldhavethemdountoyou.

Averysimple,smalldesignprinciplefromJesusChrist,aNazareneJewfromtwothousandyearsago.Andthisdesignprincipletheoreticallyiswhatdrivesanumberofreligionsthathavebeenbuiltontopoftheteachingsofthisprinciple.Theprinciplesandthepracticessometimesgooutofsync.

Here’sanexamplefromfiction.WhenGeorgeOrwellwroteAnimalFarmhehadafictionalsocietyandthatfictionalsocietywasbuiltuponadesignprinciple.Inthiscasethedesignprinciplewas:

Fourlegsgood,twolegsbad.

What’sinterestingisthatinAnimalFarm,asthesocietychanges,asthesocietyevolvesfortheworse,thedesignprinciplechangesalongwithitsothedesignprinciplecomesfourlegsgood,twolegsbetterastheanimalfarmitselfchangesbutit’sinterestingtoseethisinworksoffiction.

Thereisanotherworkoffictionthathasthreedesignprinciplesbakedinandthat’sfromthecanonofworkfromIsaacAsimovonrobotics.Hecoinedthetermroboticsandhebasicallyensconcedthesethreelawsofrobotics,threefairlysimpledesignprinciplesbutthenbuildawholecanonofwouldaroundthem,aboutfiftybooks,eachpermutationsexaminingthesedesignprinciplesfromdifferentaspects.You’reprobablyfamiliarwiththethreelawsofroboticsI’msure.

Arobotmaynotinjureahumanbeingor,throughinaction,allowahumanbeingtocometoharm.

Arobotmustobeyanyordersgiventoitbyhumanbeings,exceptwheresuchorderswouldconflictwiththeFirstLaw.

ArobotmustprotectitsownexistenceaslongassuchprotectiondoesnotconflictwiththeFirstorSecondLaw.

Thisis,Ithink,thefirstexampleinfictionofdesignprinciplesforapieceofsoftware.Inthiscaseitwouldbeapriceofsoftwaretorunapositronicbraininarobotthat’sdesignedtothethreesimpledesignprinciples.ButIthinkthismightbethestartofactuallyhavingdesignprinciplesforsoftware.Andsincethenweseedesignprinciplesforalotofreallygoodsoftware.

TimBerners-Leewho,asyouknow,co-inventedtheweb.HehasadocumentontheW3CwebsitewherehekeepshisownsetofpersonaldesignprinciplesataURL.Theyarekindofsprawling,therearealotofthemthere,headdstothem,headjuststhem,hetakesthingsawayastimegoesonbutIthinkit’sareallygoodideatohaveapersonalsetofdesignprinciplessomewhere.

Actually,BertBos,co-inventorofCSS,he’sgotgreatdocumentontheW3Cwebsitethatiskindofametadesignprinciplesdocument.Likehowtodesignbuildingaformat,whetherit’sCSSoranythingelse.Itiswellworthreading.

SoifyourootaroundtheW3CsiteyoufindabunchofthesedesignprinciplesincludingTImBerners-Lee’spersonalonesandyouseethewatchwordshe’stakenfromschoolsofsoftwareengineering:

decentralisation,tolerance,simplicity,modularity.Thesearekeywatchwordsthathekeepsinmindastheycomeupwithformats.

You’reallprettyfamiliarwiththeworkofTimBerners-Leeasyouuseiteveryday.Heinventedtheweb,co-inventedthewebwithRobertCailliau,andaswellasinventingthewebitselfhealsocameupwiththelanguagethatweuseeverydayonthewebandthatlanguageisofcourseHTML:

HyperTextMarkupLanguage.

HTML

ThisisanearlyhistoryofHTML,itstartedwithversiontwopointzero.ThereneverwasaHTMLone.IfanyoneevertellsyoutheyhavebeendoingHTMLsinceversionone,theyarebullshittingyou.TherewasadocumentcalledHTMLTagsthatcontainedahandfuloftagsthatstillexiststodaybutitwasn’tanofficialspecification.

Thiswholeideaofusingtags,anglebrackets,‘p’or‘h1’orwhathaveyou;

thatisn’tsomethingthanTimBerners-Leecameupwith.HewasbasicallytakinganexistingvocabularyfromSGML,theparticularversionofSGMLthatwasinuseatCERNatthetime.Soevenbackthenhewasn’tcreatingthingsfromscratch;

that’sanimportantlessonthatyoucanstillseeintheevolutionofHTML.Buildonwhat’scomebeforeratherthantryingtobuildsomethingfromscratch.

SothisHTMLTagsdocumentwasthefirstversionofHTMLbutwasn’tanofficialversion.ThefirstofficialversionwasHTML2.0whichdidn’tcomefromtheW3C.HTML2.0wasfromtheIETF,theInternetEngineeringTaskForce.TheywereresponsibleforputtingoutalotofstandardsbeforetheW3Creallystartedoff.ButfromversionthreeonwardsitwasattheW3C,theWorldWideWebConsortium,wherelaterversionsofHTMLwerespecced.

Therewassomefairlyrapidmovementinthenineties.Asyoucansee,theninetieswereaprettyturbulenttimeforanyonebuildingwebsitesbackthen.Wehadthebrowserwars,itwasprettymessy.Wehadalotofproprietaryshitbeingthrownintobrowsers.Theyweretryingtocompeteonhavingthebestproprietaryshit.Itwaskindofamessytimeanditwasn’tclearatallatthistimeifHTMLwasevengoingtobearoundandifHTMLwasgoingtolastastheformatfortheweb.

Youcanseeitevolvedfairlyquickly,3.2,4.0,4.01from1997to1999;

veryrapidevolution.Whathappenedwith4.01istheW3Csteppedback,lookedatitandsaid“Okay,thisisgood,wearedonewithHTML;

HTML4.01isthefinalversionofHTML,wedon’tneedaHTMLworkinggroupanymore.”

Theydidn’tstopworkingonthelanguagebutitwasnolongerHTMLtheywereinterestedin.RightafterHTMl4.01,theycameupwithXHTML1.0.ItsoundscompletelydifferentbutactuallyXHTML1.0wasthesameasHTML4.01.Imeanliterally,thecontentsofthespecificationwerethesame,thevocabularywasthesame,allthesameelements,allthesameattributes.Theonlydifference,theonlydifference,wasthatinXHTML1.0youwoulduseXMLsyntax.Sothatmeantallyourattributeshadtobelowercase,allyourelementshadtobelowercase,allyourattributeshadtobequoted,youhadtoremembertouseclosingtagsandyouhadtoselfclosetagslikeimgandbr.

Fromthepointofviewofthecont