HTML5 Standard Learning-Introduction

The front-end groups are quite busy recently, but I found that most of the discussions are javascriptIssues related to css, it seems that when everyone is trying to create various interactions and styles, they have forgotten the foundation of it all - HTML

In fact, I like HTML very much and feel that this language is far better than XML. It's interesting. Its flexibility and lightness are far from the extreme standard of XML. At the same time, because of its extremely small scope and limited tags, HTML has its own certainties.

The first part of this series will introduce some basic concepts in HTML5 in a very short space, and:

• Only care about the language of HTML, other javascript or css will not be involved at all

• ##Only focus on HTML, XHTML will be briefly introduced, but will not be explained in detail. XHTML has stricter specifications than HTML. For browser parsing, it can be considered a subset of HTML.

## mainly refers to the official documentation of whatwg, and is based on the current version. The compatibility of mainstream browsers has been evaluated.

• ##The introduction is all about basic concepts and will not involve implementation details such as document parsing, DOM tree construction, and script execution.

• ##After this, some technical details related to the operation of the browser, such as script parsing and execution, may be extracted for more in-depth discussion

. If you feel that HTML is uncomfortable because the start tag and end tag can be omitted casually and it is too irregular, then this series will tell you that there are very strict rules for omitting tags in HTML...

If you think HTML is simple , at worst, write it according to XML, then this series will tell you that HTML is full of traps. Even if you don’t consider the implementation of each browser, you may not be able to safely walk through this minefield...

Before starting this series, there are several very important concepts that need to be introduced. There are many concepts in HTML. For details, see the Terminology chapter, but some of them are not widely cited in the reference manual, only a small part of them. Blocks have a familiar meaning:

browsing context - browsing context

• is the page we usually see. To be precise, the browsing context is a Environment, in this environment, HTML will be parsed and constructed, CSS styles will be calculated and applied, javascript scripts will be loaded and executed, and finally content that can be seen by end users will be displayed.

Generally speaking, the contexts we most often come into contact with are as follows:

• A browser window, such as an IE6 window.

• A tab in a multi-tab browser, Firefox, Chrome and other browsers do this.

• An

element is also an independent browsing context.

• In a frameset, a

element will also form an independent browsing context.

• New line-new line

• As learned in basic computer courses, HTML defines three types of line breaks:

Different systems have their default line break outputs. HTML regulations ensure that browsers can correctly parse the three mainstream line break methods.

• Character U+000D, which is the \r character.

• Character U+000A, which is the \n character.

• The character U+000D is followed by U+000A, which is a \r\nstring.

• Space-space

• Space plays a very important role in HTML. For example, the attributes of an element can be separated by separated by spaces. Under normal circumstances, developers will press the space bar to enter a space. When there are many attributes, they may use Enter to arrange the attributes better. But probably few people will think about why the effect of carriage return is the same as that of spaces. What other characters can HTML parse as spaces?

Regarding the problem of spaces, jQuery has also committed this problem, and this problem still exists today. Line 1738 of jQuery 1.5.1 defines a regular expression
• /[\n\t\r]/g

  , which is used to separate the class attributes of elements by spaces. In version 1.4.4, this regular expression is

  /[\n\t]/g

  , which obviously misses \r. This BUG item illustrates this problem. Of course, it is a pity that version 1.5.1 still does not take care of all the space characters in the standard, that is, it does not handle the U+000C page break.

##The characters U+0020 are ordinary spaces.

• The character U+0009 is the \thorizontal tab character.

• The character U+000A is the \nline break character.

• The character U+000D is the \r carriage return character.

• Character U+000C, this is a page break and is rarely seen.

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