HTML5 for Web Designers

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贡献于2012-12-01

字数:0 关键词: 前端技术 HTML

HTML5 FOR WEB DESIGNERS Brief books for people who make websites N o. 1 HTML5 is the longest HTML specification ever written. It is also the most powerful, and in some ways, the most confusing. What do accessible, content-focused standards-based web designers and front-end developers need to know? And how can we harness the power of HTML5 in today’s browsers? In this brilliant and entertaining user’s guide, Jeremy Keith cuts to the chase with crisp, clear, practical examples, and his patented wit and charm. Crack open this book after you fasten your seatbelt in Boston. Before you land in Chicago, you’ll stop worrying and finally, fully understand HTML5. As usual, Mr. Keith takes a complex topic and eloquently describes it for the rest of us.” —Dan CeD e m C erholm, author of Handcrafted CSS and Bulletproof Web Design With superhuman ease and wit, Jeremy Keith always makes the densest technical concepts seem approachable, intuitive, and—dare I say it—fun. He’s done it again with HTML5.” — than ar otte, co-author of Designing with Web Standards, Third Edition, and Handcrafted CSS “ “ HTML5 FOR WEB DESIGNERS Jeremy Keith Foreword by Jeffrey Zeldman HTML5 FOR WEB DESIGNERS Jeremy Keith D o wnload from Wow! eBook Copyright © 2010 by Jeremy Keith All rights reserved Publisher: Jeffrey Zeldman Designer: Jason Santa Maria Editor: Mandy Brown Technical Editor: Ethan Marcotte Copyeditor: Krista Stevens ISBN 978-0-9844425-0-8 A Book Apart New York, New York http://books.alistapart.com 10 9 8 7 6 5 4 3 TABLE OF CONTENTS chapter 1 A Brief History of Markup1 chapter 2 The Design of HTML59 chapter 3 Rich Media22 chapter 4 Web Forms 2.040 chapter 5 Semantics56 chapter 6 Using HTML5 Today78 Index86 FOREWORD When Mandy Brown, Jason Santa Maria and I formed A Book Apart, one topic burned uppermost in our minds, and there was only one author for the job. Nothing else, not even “real fonts” or CSS3, has stirred the standards-based design community like the imminent arrival of HTML5. Born out of dissatisfaction with the pacing and politics of the W3C, and conceived for a web of applications (not just documents), this new edition of the web’s lingua franca has in equal measure excited, angered, and confused the web design community. Just as he did with the DOM and JavaScript, Jeremy Keith has a unique ability to illuminate HTML5 and cut straight to what matters to accessible, standards-based designer-developers. And he does it in this book, using only as many words and pictures as are needed. There are other books about HTML5, and there will be many more. There will be 500 page technical books for application developers, whose needs drove much of HTML5’s develop- ment. There will be even longer secret books for browser makers, addressing technical challenges that you and I are blessed never to need to think about. But this is a book for you—you who create web content, who mark up web pages for sense and semantics, and who design accessible interfaces and experiences. Call it your user guide to HTML5. Its goal—one it will share with every title in the forthcoming A Book Apart catalog—is to shed clear light on a tricky subject, and do it fast, so you can get back to work. —Jeffrey Zeldman D o wnload from Wow! eBook 1 A BRIEF HISTORY OF MARKUP 1 A BRIEF HISTORY OF MARKUP HTML is THe unifying Language of the World Wide Web. Using just the simple tags it contains, the human race has cre- ated an astoundingly diverse network of hyperlinked docu- ments, from Amazon, eBay, and Wikipedia, to personal blogs and websites dedicated to cats that look like Hitler. HTML5 is the latest iteration of this lingua franca. While it is the most ambitious change to our common tongue, this isn’t the first time that HTML has been updated. The language has been evolving from the start. As with the web itself, the HyperText Markup Language was the brainchild of Sir Tim Berners-Lee. In 1991 he wrote a doc- ument called “HTML Tags” in which he proposed fewer than two dozen elements that could be used for writing web pages. Sir Tim didn’t come up with the idea of using tags consisting of words between angle brackets; those kinds of tags already existed in the SGML (Standard Generalized Markup Language) 2 HTML5 FOR WEB DESIGNERS format. Rather than inventing a new standard, Sir Tim saw the benefit of building on top of what already existed—a trend that can still be seen in the development of HTML5. FROM IETF TO W3C: THE ROAD TO HTML 4 There was never any such thing as HTML 1. The first official specification was HTML 2.0, published by the IETF, the Internet Engineering Task Force. Many of the features in this specification were driven by existing implementations. For example, the market-leading Mosaic web browser of 1994 already provided a way for authors to embed images in their documents using an tag. The img element later appeared in the HTML 2.0 specification. The role of the IETF was superceded by the W3C, the World Wide Web Consortium, where subsequent iterations of the HTML standard have been published at http://www.w3.org. The latter half of the nineties saw a flurry of revisions to the specification until HTML 4.01 was published in 1999. At that time, HTML faced its first major turning point. XHTML 1: HTML AS XML After HTML 4.01, the next revision to the language was called XHTML 1.0. The X stood for “eXtreme” and web developers were required to cross their arms in an X shape when speak- ing the letter. No, not really. The X stood for “eXtensible” and arm crossing was entirely optional. The content of the XHTML 1.0 specification was identical to that of HTML 4.01. No new elements or attributes were added. The only difference was in the syntax of the language. Whereas HTML allowed authors plenty of freedom in how 3 A BRIEF HISTORY OF MARKUP they wrote their elements and attributes, XHTML required authors to follow the rules of XML, a stricter markup language upon which the W3C was basing most of their technologies. Having stricter rules wasn’t such a bad thing. It encouraged authors to use a single writing style. Whereas previously tags and attributes could be written in uppercase, lowercase, or any combination thereof, a valid XHTML 1.0 document re- quired all tags and attributes to be lowercase. The publication of XHTML 1.0 coincided with the rise of browser support for CSS. As web designers embraced the emergence of web standards, led by The Web Standards Project, the stricter syntax of XHTML was viewed as a “best practice” way of writing markup. Then the W3C published XHTML 1.1. While XHTML 1.0 was simply HTML reformulated as XML, XHTML 1.1 was real, honest-to-goodness XML. That meant it couldn’t be served with a mime-type of text/html. But if authors published a document with an XML mime-type, then the most popular web browser in the world at the time— Internet Explorer—couldn’t render the document. It seemed as if the W3C were losing touch with the day-to-day reality of publishing on the web. XHTML 2: OH, WE’RE NOT GONNA TAKE IT! If Dustin Hoffman’s character in The Graduate had been a web designer, the W3C would have said one word to him, just one word: XML. As far as the W3C was concerned, HTML was finished as of version 4. They began working on XHTML 2, designed to lead the web to a bright new XML-based future. 4 HTML5 FOR WEB DESIGNERS Although the name XHTML 2 sounded very similar to XHTML 1, they couldn’t have been more different. Unlike XHTML 1, XHTML 2 wasn’t going to be backwards compat- ible with existing web content or even previous versions of HTML. Instead, it was going to be a pure language, unbur- dened by the sloppy history of previous specifications. It was a disaster. THE SCHISM: WHATWG TF? A rebellion formed within the W3C. The consortium seemed to be formulating theoretically pure standards unrelated to the needs of web designers. Representatives from Opera, Apple, and Mozilla were unhappy with this direction. They wanted to see more emphasis placed on formats that allowed the cre- ation of web applications. Things came to a head in a workshop meeting in 2004. Ian Hickson, who was working for Opera Software at the time, proposed the idea of extending HTML to allow the creation of web applications. The proposal was rejected. The disaffected rebels formed their own group: the Web Hypertext Application Technology Working Group, or WHATWG for short. FROM WEB APPS 1.0 TO HTML5 From the start, the WHATWG operated quite differently than the W3C. The W3C uses a consensus-based approach: issues are raised, discussed, and voted on. At the WHATWG, issues are also raised and discussed, but the final decision on what goes into a specification rests with the editor. The editor is Ian Hickson. 5 A BRIEF HISTORY OF MARKUP On the face of it, the W3C process sounds more democratic and fair. In practice, politics and internal bickering can bog down progress. At the WHATWG, where anyone is free to contribute but the editor has the last word, things move at a faster pace. But the editor doesn’t quite have absolute power: an invitation-only steering committee can impeach him in the unlikely event of a Strangelove scenario. Initially, the bulk of the work at the WHATWG was split into two specifications: Web Forms 2.0 and Web Apps 1.0. Both specifications were intended to extend HTML. Over time, they were merged into a single specification called simply HTML5. REUNIFICATION While HTML5 was being developed at the WHATWG, the W3C continued working on XHTML 2. It would be inaccurate to say that it was going nowhere fast. It was going nowhere very, very slowly. In October 2006, Sir Tim Berners-Lee wrote a blog post in which he admitted that the attempt to move the web from HTML to XML just wasn’t working. A few months later, the W3C issued a new charter for an HTML Working Group. Rather than start from scratch, they wisely decided that the work of the WHATWG should be used as the basis for any future version of HTML. All of this stopping and starting led to a somewhat confusing situation. The W3C was simultaneously working on two different, incompatible types of markup: XHTML 2 and HTML 5 (note the space before the number five). Meanwhile a separate organization, the WHATWG, was working on a specification called HTML5 (with no space) that would be used as a basis for one of the W3C specifications! 6 HTML5 FOR WEB DESIGNERS Any web designers trying to make sense of this situation would have had an easier time deciphering a movie marathon of Memento, Primer, and the complete works of David Lynch. XHTML IS DEAD: LONG LIVE XHTML SYNTAX The fog of confusion began to clear in 2009. The W3C an- nounced that the charter for XHTML 2 would not be re- newed. The format had been as good as dead for several years; this announcement was little more than a death certificate. Strangely, rather than passing unnoticed, the death of XHTML 2 was greeted with some mean-spirited gloating. XML naysayers used the announcement as an opportunity to deride anyone who had ever used XHTML 1—despite the fact that XHTML 1 and XHTML 2 have almost nothing in common. Meanwhile, authors who had been writing XHTML 1 in order to enforce a stricter writing style became worried that HTML5 would herald a return to sloppy markup. As you’ll soon see, that’s not necessarily the case. HTML5 is as sloppy or as strict as you want to make it. THE TIMELINE OF HTML5 The current state of HTML5 isn’t as confusing as it once was, but it still isn’t straightforward. There are two groups working on HTML5. The WHATWG is creating an HTML5 specification using its process of “commit then review.” The W3C HTML Working Group is taking that specification and putting it through its process of “review then commit.” As you can imagine, it’s an uneasy alliance. Still, there seems to finally be some consensus about that pesky D o wnload from Wow! eBook 7 A BRIEF HISTORY OF MARKUP “space or no space?” question (it’s HTML5 with no space, just in case you were interested). Perhaps the most confusing issue for web designers dipping their toes into the waters of HTML5 is getting an answer to the question, “when will it be ready?” In an interview, Ian Hickson mentioned 2022 as the year he expected HTML5 to become a proposed recommendation. What followed was a wave of public outrage from some web designers. They didn’t understand what “proposed recom- mendation” meant, but they knew they didn’t have enough fingers to count off the years until 2022. The outrage was unwarranted. In this case, reaching a status of “proposed recommendation” requires two complete imple- mentations of HTML5. Considering the scope of the specifica- tion, this date is incredibly ambitious. After all, browsers don’t have the best track record of implementing existing standards. It took Internet Explorer over a decade just to add support for the abbr element. The date that really matters for HTML5 is 2012. That’s when the specification is due to become a “candidate recommenda- tion.” That’s standards-speak for “done and dusted.” But even that date isn’t particularly relevant to web design- ers. What really matters is when browsers start supporting features. We began using parts of CSS 2.1 as soon as browsers started shipping with support for those parts. If we had wait- ed for every browser to completely support CSS 2.1 before we started using any of it, we would still be waiting. It’s no different with HTML5. There won’t be a single point in time at which we can declare that the language is ready to use. Instead, we can start using parts of the specification as web browsers support those features. 8 HTML5 FOR WEB DESIGNERS Remember, HTML5 isn’t a completely new language created from scratch. It’s an evolutionary rather than revolutionary change in the ongoing story of markup. If you are currently creating websites with any version of HTML, you’re already using HTML5. 9 THE DESIGN OF HTML5 2 THE DESIGN OF HTML5 THe frencH revoLuTion was an era of extreme political and social change. Revolutionary fervor was applied to time itself. For a brief period, the French Republic introduced a decimal time system, with each day divided into ten hours and each hour divided into one hundred minutes. It was thor- oughly logical and clearly superior to the sexagesimal system. Decimal time was a failure. Nobody used it. The same could be said for XHTML 2. The W3C rediscovered the lesson of post-revolutionary France: changing existing behavior is very, very difficult. DESIGN PRINCIPLES Keen to avoid the mistakes of the past, the WHATWG drafted a series of design principles to guide the development of HTML5. One of the key principles is to “Support existing con- tent.” That means there’s no Year Zero for HTML5. 10 HTML5 FOR WEB DESIGNERS Where XHTML 2 attempted to sweep aside all that had come before, HTML5 builds upon existing specifications and imple- mentations. Most of HTML 4.01 has survived in HTML5. Some of the other design principles include “Do not reinvent the wheel,” and “Pave the cowpaths,” meaning, if there’s a widespread way for web designers to accomplish a task—even if it’s not necessarily the best way—it should be codified in HTML5. Put another way, “If it ain’t broke, don’t fix it.” Many of these design principles will be familiar to you if you’ve ever dabbled in the microformats community (http:// microformats.org). The HTML5 community shares the same pragmatic approach to getting a format out there, without worrying too much about theoretical problems. This attitude is enshrined in the design principle of “Priority of constituencies,” which states, “In case of conflict, consider users over authors over implementers over specifiers over theoretical purity.” Ian Hickson has stated on many occasions that browser makers are the real arbiters of what winds up in HTML5. If a browser vendor refuses to support a particular proposal, there’s no point in adding that proposal to the specification because then the specification would be fiction. According to the priority of constituencies, we web designers have an even stronger voice. If we refuse to use part of the specification, then the specification is equally fictitious. KEEPING IT REAL The creation of HTML5 has been driven by an ongoing inter- nal tension. On the one hand, the specification needs to be powerful enough to support the creation of web applications. On the other hand, HTML5 needs to support existing con- tent, even if most existing content is a complete mess. If the 11 THE DESIGN OF HTML5 specification strays too far in one direction, it will suffer the same fate as XHTML 2. But if it goes too far in the other direc- tion, the specification will enshrine tags and tables for layout because, after all, that’s what a huge number of web pages are built with. It’s a delicate balancing act that requires a pragmatic, level- headed approach. ERROR HANDLING The HTML5 specification doesn’t just declare what browsers should do when they are processing well-formed markup. For the first time, a specification also defines what browsers should do when they are dealing with badly formed documents. Until now, browser makers have had to individually figure out how to deal with errors. This usually involved reverse engineering whatever the most popular browser was doing— not a very productive use of their time. It would be better for browser makers to implement new features rather than waste their time duplicating the way their competitors handle mal- formed markup. Defining error handling in HTML5 is incredibly ambitious. Even if HTML5 had exactly the same elements and attributes as HTML 4.01, with no new features added, defining error handling by 2012 would still be a Sisyphean task. Error handling might not be of much interest to web design- ers, especially if we are writing valid, well-formed documents to begin with, but it’s very important for browser makers. Whereas previous markup specifications were written for authors, HTML5 is written for authors and implementers. Bear that in mind when perusing the specification. It explains why the HTML5 specification is so big and why it seems to have been written with a level of detail normally reserved for 12 HTML5 FOR WEB DESIGNERS trainspotters who enjoy a nice game of chess while indexing their stamp collection. GIVE IT TO ME STRAIGHT, DOCTYPE A Document Type Declaration, or doctype for short, has traditionally been used to specify which particular flavor of markup a document is written in. The doctype for HTML 4.01 looks like this (line wraps marked »): Here’s the doctype for XHTML 1.0: They’re not very human-readable, but, in their own way, they are simply saying “this document is written in HTML 4.01,” or “this document is written in XHTML 1.0.” You might expect the doctype declaring “this document is written in HTML5” would have the number five in it some- where. It doesn’t. The doctype for HTML5 looks like this: It’s so short that even I can memorize it. But surely this is madness! Without a version number in the doctype, how will we specify future versions of HTML? 13 THE DESIGN OF HTML5 When I first saw the doctype for HTML5, I thought it was the height of arrogance. I asked myself, “Do they really believe that this will be the final markup specification ever written?” It seemed to be a textbook case of Year Zero thinking. In fact, though, the doctype for HTML5 is very pragmatic. Because HTML5 needs to support existing content, the doc- type could be applied to an existing HTML 4.01 or XHTML 1.0 document. Any future versions of HTML will also need to support the existing content in HTML5, so the very concept of applying version numbers to markup documents is flawed. The truth is that doctypes aren’t even important. Let’s say you serve up a document with a doctype for HTML 4.01. If that document includes an element from another specifica- tion, such as HTML 3.2 or HTML5, a browser will still render that part of the document. Browsers support features, not doctypes. Document Type Declarations were intended for validators, not browsers. The only time that a browser pays any attention to a doctype is when it is performing “doctype switching”— a clever little hack that switches rendering between quirks mode and standards mode depending on the presence of a decent doctype. The minimum information required to ensure that a browser renders using standards mode is the HTML5 doctype. In fact, that’s the only reason to include the doctype at all. An HTML document written without the HTML5 doctype can still be valid HTML5. KEEPING IT SIMPLE The doctype isn’t the only thing that has been simplified in HTML5. D o wnload from Wow! eBook 14 HTML5 FOR WEB DESIGNERS If you want to specify the character encoding of a markup document, the best way is to ensure that your server sends the correct Content-Type header. If you want to be doubly certain, you can also specify the character set using a tag. Here’s the meta declaration for a document written in HTML 4.01: Here’s the much more memorable way of doing the same thing in HTML5: As with the doctype, this simplified character encoding contains the minimum number of characters needed to be interpreted by browsers. The Browsers don’t need that attribute. They will assume that the script is written in JavaScript, the most popular scripting lan- guage on the web (let’s be honest: the only scripting language on the web): Likewise, you don’t need to specify a type value of “text/css” every time you link to a CSS file: 15 THE DESIGN OF HTML5 You can simply write: SYNTAX: MARKING IT UP YOUR WAY Some programming languages, such as Python, enforce a particular way of writing instructions. Using spaces to indent code is mandatory—the white space is significant. Other pro- gramming languages, such as JavaScript, don’t pay any atten- tion to formatting—the white space at the start of a line isn’t significant. If you’re looking for a cheap evening’s entertainment, get an array of programmers into the same room and utter the words “significant white space.” You can then spend hours warming yourself by the ensuing flame war. There’s a fundamental philosophical question at the heart of the significant white space debate: should a language enforce a particular style of writing, or should authors be free to write in whatever style they like? Markup doesn’t require significant white space. If you want to add a new line and an indentation every time you nest an element, you can do so, but browsers and validators don’t re- quire it. This doesn’t mean that markup is a free-for-all. Some flavors of markup enforce a stricter writing style than others. Before XHTML 1.0, it didn’t matter if you wrote tags in upper- case or lowercase. It didn’t matter whether or not you quoted attributes. For some elements, it didn’t even matter whether you included the closing tag. XHTML 1.0 enforces the syntax of XML. All tags must be writ- ten in lowercase. All attributes must be quoted. All elements 16 HTML5 FOR WEB DESIGNERS must have a closing tag. In the special case of standalone ele- ments such as br, the requirement for a closing tag is replaced with a requirement for a closing slash:
. With HTML5, anything goes. Uppercase, lowercase, quoted, unquoted, self-closing or not; it’s entirely up to you. I’ve been using the XHTML 1.0 doctype for years. I like the fact that I must write in one particular style and I like the way that the W3C validator enforces that style. Now that I’m using HTML5, it’s up to me to enforce the style I want. I can see why some people don’t like the looseness of the HTML5 syntax. It seems like it’s turning the clock back on years of best practices. Some people have even said that the lax syntax of HTML5 is encouraging bad markup. I don’t think that’s true, but I can see why it’s a concern. It’s as if a programming language that enforced significant white space suddenly changed over to a more forgiving rule set. Personally, I’m okay with the casual syntax of HTML5. I’ve come to terms with having to enforce my own preferred writ- ing style myself. But I would like to see more tools that would allow me to test my markup against a particular style. In the world of programming, these are called lint tools: programs that flag up suspect coding practices. A lint tool for markup would be different than a validator, which checks against a doctype; but it would be wonderful if the two could be com- bined into one lean, mean validating linting machine. Whosoever shall program such a device will earn the undying respect and admiration of web designers everywhere. WE DON’T USE THAT KIND OF LANGUAGE In past versions of HTML, whenever a previously existing element or attribute was removed from the specification, the process was called deprecation. Web designers were advised 17 THE DESIGN OF HTML5 not to use deprecated elements, or send them Christmas cards, or even mention them in polite company. There are no deprecated elements or attributes in HTML5. But there are plenty of obsolete elements and attributes. No, this isn’t a case of political correctness gone mad. “Obso- lete” has a subtly different meaning from “deprecated.” Because HTML5 aims to be backwards compatible with exist- ing content, the specification must acknowledge previously existing elements even when those elements are no longer in HTML5. This leads to a slightly confusing situation where the specification simultaneously says, “authors, don’t use this element” and, “browsers, here’s how you should render this element.” If the element were deprecated, it wouldn’t be men- tioned in the specification at all; but because the element is obsolete, it is included for the benefit of browsers. Unless you’re building a browser, you can treat obsolete ele- ments and attributes the same way you would treat deprecated elements and attributes: don’t use them in your web pages and don’t invite them to cocktail parties. If you insist on using an obsolete element or attribute, your document will be “non-conforming.” Browsers will render everything just fine, but you might hear a tut-ing sound from the website next door. So long, been good to know ya The frame, frameset, and noframes elements are obsolete. They won’t be missed. The acronym element is obsolete, thereby freeing up years of debating time that can be better spent calculating the angel-density capacity of standard-sized pinheads. Do not mourn the acronym element; just use the abbr element in- stead. Yes, I know there’s a difference between acronyms and 18 HTML5 FOR WEB DESIGNERS abbreviations—acronyms are spoken as single words, like NATO and SCUBA—but just remember: all acronyms are ab- breviations, but not all abbreviations are acronyms. Presentational elements such as font, big, center, and strike are obsolete in HTML5. In reality, they’ve been obsolete for years; it’s much easier to achieve the same presentational effects using CSS properties such as font-size and text- align. Similarly, presentational attributes such as bgcolor, cellspacing, cellpadding, and valign are obsolete. Just use CSS instead. Not all presentational elements are obsolete. Some of them have been through a re-education program and given one more chance. TURN & FACE THE STRANGE (CH-CH-CHANGES) The big element is obsolete but the small element isn’t. This apparent inconsistency has been resolved by redefining what small means. It no longer has the presentational connotation, “render this at a small size.” Instead, it has the semantic value, “this is the small print,” for legalese, or terms and conditions. Of course, nine times out of ten you will want to render the small print at a small size, but the point is that the purely pre- sentational meaning of the element has been superseded. The b element used to mean, “render this in bold.” Now it is used for some text “to be stylistically offset from the normal prose without conveying any extra importance.” If the text has any extra importance, then the strong element would be more appropriate. Similarly, the i element no longer means “italicize.” It means the text is “in an alternate voice or mood.” Again, the element doesn’t imply any importance or emphasis. For emphasis, use the em element. 19 THE DESIGN OF HTML5 These changes might sound like word games. They are; but they also help to increase the device-independence of HTML5. If you think about the words “bold” and “italic,” they only make sense for a visual medium such as a screen or a page. By removing the visual bias from the definitions of these elements, the specification remains relevant for non-visual user agents such as screen readers. It also encourages design- ers to think beyond visual rendering environments. Out of cite The cite element has been redefined in HTML5. Where it previously meant “a reference to other sources,” it now means “the title of a work.” Quite often, a cited reference will be the title of a work, such as a book or a film, but the source could just as easily be a person. Before HTML5, you could mark up that person’s name using cite. Now that’s expressly forbid- den—so much for backwards compatibility. The justification for this piece of revisionism goes something like this: browsers italicize the text between tags; titles of works are usually italicized; people’s names aren’t usually italicized; therefore the cite element shouldn’t be used for marking up people’s names. That’s just plain wrong. I’m in favor of HTML5 taking its lead from browsers, but this is a case of the tail wagging the dog. Fortunately, no validator can possibly tell whether the text between opening and closing tags refers to a person or not, so there’s nothing to stop us web designers from using the cite element in a sensible, backwards compatible way. The a element on steroids While the changes to previously existing elements involve creative wordplay, there’s one element that’s getting a super- charged makeover in HTML5. D o wnload from Wow! eBook 20 HTML5 FOR WEB DESIGNERS The a element is, without a doubt, the most important element in HTML. It turns our text into hypertext. It is the connective tissue of the World Wide Web. The a element has always been an inline element. If you want- ed to make a headline and a paragraph into a hyperlink, you would have to use multiple a elements:

About me

Find out what makes me tick.

In HTML5, you can wrap multiple elements in a single a element:

About me

Find out what makes me tick.

The only caveat is that you can’t nest an a element within an- other a element. Wrapping multiple elements in a single a element might seem like a drastic change, but most browsers won’t have to do much to support this new linking model. They already sup- port it even though this kind of markup has never been tech- nically legal until now. This seems slightly counter-intuitive: Surely the browsers should be implementing an existing specification? Instead, the newest specification is documenting what browsers are already doing. SHINY NEW TOYS: JAVASCRIPT APIs If you’re looking for documentation on CSS, you go to the CSS specifications. If you’re looking for documentation on markup, you go to the HTML specifications. But where 21 THE DESIGN OF HTML5 do you go for documentation on JavaScript APIs such as document.write, innerHTML, and window.history? The JavaScript specification is all about the programming lan- guage—you won’t find any browser APIs there. Until now, browsers have been independently creating and implementing JavaScript APIs, looking over one another’s shoulders to see what the others are doing. HTML5 will docu- ment these APIs once and for all, which should ensure better compatibility. It might sound strange to have JavaScript documentation in a markup specification, but remember that HTML5 started life as Web Apps 1.0. JavaScript is an indispensable part of making web applications. Entire sections of the HTML5 specification are dedicated to new APIs for creating web applications. There’s an Undo- Manager that allows the browser to keep track of changes to a document. There’s a section on creating Offline Web Applica- tions using a cache manifest. Drag and drop is described in detail. As always, if there is an existing implementation, the specifica- tion will build upon it rather than reinvent the wheel. Micro- soft’s Internet Explorer has had a drag and drop API for years, so that’s the basis for drag and drop in HTML5. Unfortunately, the Microsoft API is—to put it mildly—problematic. Maybe reinventing the wheel isn’t such a bad idea if all you have to work with is a square wheel. The APIs in HTML5 are very powerful. They are also com- pletely over my head. I’ll leave it to developers smarter than me to write about them. The APIs deserve their own separate book. Meanwhile, there’s still plenty of new stuff in HTML5 for us web designers to get excited about. This excitement com- mences in the very next chapter. 22 HTML5 FOR WEB DESIGNERS 3 RICH MEDIA THe HisTory of THe web is punctuated with technological improvements. One of the earliest additions to HTML was the img element, which fundamentally altered the web. Then, the introduction of JavaScript allowed the web to become a more dynamic environment. Later, the proliferation of Ajax made the web a viable option for full-fledged applications. Web standards have advanced so much that it’s now possible to build almost anything using HTML, CSS, and JavaScript— almost anything. There are some gaps in the web standards palette. If you want to publish text and images, HTML and CSS are all you need. But if you want to publish audio or video, you’ll need to use a plug-in technology such as Flash or Silverlight. “Plug-in” is an accurate term for these technologies—they 23 RICH MEDIA help to fill the holes on the web. They make it relatively easy to get games, films, and music online. But these technologies are not open. They are not created by the community. They are under the control of individual companies. Flash is a powerful technology, but using it sometimes feels like a devil’s bargain. We gain the ability to publish rich media on the web, but in doing so, we lose some of our independence. HTML5 is filling in the gaps. As such, it is in direct competi- tion with proprietary technologies like Flash and Silverlight. But instead of requiring a plug-in, the rich media elements in HTML5 are native to the browser. CANVAS When the Mosaic browser added the ability to embed images within web pages, it gave the web a turbo boost. But images have remained static ever since. You can create animated gifs. You can use JavaScript to update an image’s styles. You can generate an image dynamically on the server. But once an im- age has been served up to a browser, its contents cannot be updated. The canvas element is an environment for creating dynamic images. The element itself is very simple. All you specify within the opening tag are the dimensions: If you put anything between the opening and closing tags, only browsers that don’t support canvas will see it (fig 3.01): 24 HTML5 FOR WEB DESIGNERS

No canvas support? Have an old-fashioned image » instead:

a cute puppy
fig 3.01: Users without canvas support will see the image of a cute puppy. var canvas = document.getElementById('my-first-canvas'); var context = canvas.getContext('2d'); Now you can start drawing on the two-dimensional surface of the canvas element using the API documented in the HTML5 specification at http://bkaprt.com/html5/1.1 The 2D API offers a lot of the same tools that you find in a graphics program like Illustrator: strokes, fills, gradients, shad- ows, shapes, and Bézier curves. The difference is that, instead 1. The long URL: http://www.whatwg.org/specs/web-apps/current-work/ multipage/the-canvas-element.html All the hard work is done in JavaScript. First of all, you’ll need to reference the canvas element and its context. The word “context” here simply means an API. For now, the only con- text is two-dimensional: 25 RICH MEDIA of using a Graphical User Interface, you have to specify every- thing using JavaScript. Dancing about architecture: drawing with code This is how you specify that the stroke color should be red: context.strokeStyle = '#990000'; Now anything you draw will have a red outline. For example, if you want to draw a rectangle, use this syntax: strokeRect ( left, top, width, height ) If you want to draw a rectangle that’s 100 by 50 pixels in size, positioned 20 pixels from the left and 30 pixels from the top of the canvas element, you’d write this (fig 3.02): context.strokeRect(20,30,100,50); fig 3.02: A rectangle, drawn with canvas. That’s one very simple example. The 2D API provides lots of methods: fillStyle, fillRect, lineWidth, shadowColor and many more. In theory, any image that can be created in a program like Illustrator can be created in the canvas element. In practice, doing so would be laborious and could result in excessively long JavaScript. Besides, that isn’t really the point of canvas. 26 HTML5 FOR WEB DESIGNERS Canvas. Huh! What is it good for? It’s all well and good using JavaScript and canvas to create im- ages on the fly, but unless you’re a hardcore masochist, what’s the point? The real power of canvas is that its contents can be updated at any moment, drawing new content based on the actions of the user. This ability to respond to user-triggered events makes it possible to create tools and games that would have previously required a plug-in technology such as Flash. One of the first flagship demonstrations of the power of canvas came from Mozilla Labs. The Bespin application (https://bespin.mozilla.com) is a code editor that runs in the browser (fig 3.03). It is very powerful. It is very impressive. It is also a perfect example of what not to do with canvas. fig 3.03: The Bespin application, built with canvas. 27 RICH MEDIA Access denied A code editor, by its nature, handles text. The Bespin code editor handles text within the canvas element—except that it isn’t really text anymore; it’s a series of shapes that look like text. Every document on the web can be described with a Docu- ment Object Model. This DOM can have many different nodes, the most important of which are element nodes, text nodes, and attributes. Those three building blocks are enough to put together just about any document you can imagine. The canvas element has no DOM. The content drawn within canvas cannot be represented as a tree of nodes. Screen readers and other assistive technology rely on having access to a Document Object Model to make sense of a docu- ment. No DOM, no access. The lack of accessibility in canvas is a big problem for HTML5. Fortunately there are some very smart people work- ing together as a task force to come up with solutions (http:// bkaprt.com/html5/2).2 Canvas accessibility is an important issue and I don’t want any proposed solutions to be rushed. At the same time, I don’t want canvas to hold up the rest of the HTML5 spec. Clever canvas Until the lack of accessibility is addressed, it might seem as though canvas is off-limits to web designers. But it ain’t neces- sarily so. Whenever I use JavaScript on a website, I use it as an en- hancement. Visitors who don’t have JavaScript still have ac- cess to all the content, but the experience might not be quite 2. The long URL: http://www.w3.org/WAI/PF/html-task-force 28 HTML5 FOR WEB DESIGNERS as dynamic as in a JavaScript-capable environment. This multi-tiered approach, called Unobtrusive JavaScript, can also be applied to canvas. Instead of using canvas to create content, use it to recycle existing content. Suppose you have a table filled with data. You might want to illustrate the trends in the data using a graph. If the data is static, you can generate an image of a graph—using the Google Chart API, for example. If the data is editable, updating in re- sponse to user-triggered events, then canvas is a good tool for generating the changing graph. Crucially, the content repre- sented within the canvas element is already accessible in the pre-existing table element. The clever folks at Filament Group have put together a jQuery plug-in for that very situation (fig 3.04; http://bkaprt.com/ html5/3).3 There is another option. Canvas isn’t the only API for gener- ating dynamic images. SVG, Scalable Vector Graphics, is an fig 3.04: Using canvas to generate a graph from data input by users. 3. The long URL: http://www.filamentgroup.com/lab/update_to_jquery_ visualize_accessible_charts_with_html5_from_designing_with/ D o wnload from Wow! eBook 29 RICH MEDIA XML format that can describe the same kind of shapes as can- vas. Because XML is a text-based data format, the contents of SVG are theoretically available to screen readers. In practice, SVG hasn’t captured the imagination of develop- ers in the same way that canvas has. Even though canvas is the new kid on the block, it already enjoys excellent browser support. Safari, Firefox, Opera, and Chrome support canvas. There’s even a JavaScript library that adds canvas support to Internet Explorer (http://bkaprt.com/html5/4).4 Given its mantras of “pave the cowpaths,” and “don’t reinvent the wheel,” it might seem odd that the WHATWG would advocate canvas in HTML5 when SVG already exists. As is so often the case, the HTML5 specification is really just documenting what browsers already do. The canvas element wasn’t dreamt up for HTML5; it was created by Apple and implemented in Safari. Other browser makers saw what Apple was doing, liked what they saw, and copied it. It sounds somewhat haphazard, but this is often where our web standards come from. Microsoft, for example, created the XMLHttpRequest object for Internet Explorer 5 at the end of the 20th century. A decade later, every browser supports this feature and it’s now a working draft in last call at the W3C. In the Darwinian world of web browsers, canvas is spread- ing far and wide. If it can adapt for accessibility, its survival is ensured. AUDIO The first website I ever made was a showcase for my band. I wanted visitors to the site to be able to listen to the band’s songs. That prompted my journey into the underworld to investigate the many formats and media players competing 4. The long URL: http://code.google.com/p/explorercanvas/ 30 HTML5 FOR WEB DESIGNERS for my attention: QuickTime, Windows Media Player, Real Audio—I spent far too much time worrying about relative market share and cross-platform compatibility. In the intervening years, the MP3 format has won the battle for ubiquity. But providing visitors with an easy way to listen to a sound file still requires a proprietary technology. The Flash player has won that battle. Now HTML5 is stepping into the ring in an attempt to take on the reigning champion. Embedding an audio file in an HTML5 document is simple: That’s a little too simple. You probably want to be a bit more specific about what the audio should do. Suppose there’s an evil bastard out there who hates the web and all who sail her. This person probably doesn’t care that it’s incredibly rude and stupid to embed an audio file that plays automatically. Thanks to the autoplay attribute, such malevo- lent ambitions can be realized: If you ever use the autoplay attribute in this way, I will hunt you down. Notice that the autoplay attribute doesn’t have a value. This is known as a Boolean attribute, named for that grand Cork mathematician George Boole. Computer logic is based entirely on Boolean logic: an electric current is either flowing or it isn’t; a binary value is either one or zero; the result of a computation is either true or false. 31 RICH MEDIA Don’t confuse Boolean attributes with Boolean values. You’d be forgiven for thinking that a Boolean attribute would take the values “true” or “false.” Actually, it’s the very existence of the attribute that is Boolean in nature: either the attribute is in- cluded or it isn’t. Even if you give the attribute a value, it will have no effect. Writing autoplay="false" or autoplay="no thanks" is the same as writing autoplay. If you are using XHTML syntax, you can write autoplay= "autoplay". This is brought to you by the Department of Redundancy Department. When an auto-playing audio file isn’t evil enough, you can in- flict even more misery by having the audio loop forever. An- other Boolean attribute, called loop, fulfills this dastardly plan: Using the loop attribute in combination with the autoplay attribute in this way will renew my determination to hunt you down. Out of control The audio element can be used for good as well as evil. Giving users control over the playback of an audio file is a sensible idea that is easily accomplished using the Boolean attribute controls: The presence of the controls attribute prompts the browser to provide native controls for playing and pausing the audio, as well as adjusting the volume (fig 3.05). If you’re not happy with the browser’s native controls, you can create your own. Using JavaScript, you can interact with 32 HTML5 FOR WEB DESIGNERS fig 3.05: Use controls to display play, pause, and volume controls for your audio. the Audio API, which gives you access to methods such as play and pause and properties such as volume. Here’s a quick ’n’ dirty example using button elements and nasty inline event handlers (fig 3.06):
Buffering At one point, the HTML5 spec included another Boolean attribute for the audio element. The autobuffer attribute was more polite and thoughtful than the nasty autoplay attribute. It provided a way for authors to inform the browser 33 RICH MEDIA fig 3.06: The controls produced by the button elements. that—although the audio file shouldn’t play automatically—it will probably be played at some point, so the browser should start pre-loading the file in the background. This would have been a useful attribute, but unfortunately Safari went a step further. It preloaded audio files regardless of whether or not the autobuffer attribute was present. Re- member that because autobuffer was a Boolean attribute, there was no way to tell Safari not to preload the audio: autobuffer="false" was the same as autobuffer="true" or any other value (http://bkaprt.com/html5/5).5 The autobuffer attribute has now been replaced with the preload attribute. This isn’t a Boolean attribute. It can take three possible values: none, auto, and metadata. Using preload="none", you can now explicitly tell browsers not to pre-load the audio: If you only have one audio element on a page, you might want to use preload="auto", but the more audio elements you have, the more your visitors’ bandwidth is going to get ham- mered by excessive preloading. You play to-may-to, I play to-mah-to The audio element appears to be nigh-on perfect. Surely there must be a catch somewhere? There is. The problem with the audio element isn’t in the specification. The problem lies with audio formats. 5. The long URL: https://bugs.webkit.org/show_bug.cgi?id=25267 34 HTML5 FOR WEB DESIGNERS Although the MP3 format has become ubiquitous, it is not an open format. Because the format is patent-encumbered, technologies can’t decode MP3 files without paying the patent piper. That’s fine for corporations like Apple or Adobe, but it’s not so easy for smaller companies or open-source groups. Hence, Safari will happily play back MP3 files while Firefox will not. There are other audio formats out there. The Vorbis codec— usually delivered as an .ogg file—isn’t crippled by any patents. Firefox supports Ogg Vorbis—but Safari doesn’t. Fortunately, there’s a way to use the audio element with- out having to make a Sophie’s Choice between file formats. Instead of using the src attribute in the opening

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