The full syntax of the html language. html syntax and html document structure
DOM as part of the language
The concept of DOM was first introduced in HTML5. (although it existed before that, however, it was not part of the language), the HTML document is now treated as a set of objects, not tags. Therefore, how HTML5 syntax does not exist. However, when writing code, you can stick to tag markup rules, which were set in HTML 4.01 or XHTML 1.0
HTML 4.01 syntax
AT HTML before the fifth version, there were several rules for writing code:
- The loose mode used in HTML 4.01
"http://www.w3.org/TR/html4/loose.dtd"> - The strict mode used in HTML 4.01
"http://www.w3.org/TR/html4/strict.dtd"> - There was also syntax associated with frames. Frames are considered obsolete in HTML5, but many developers still use them because frames are very useful when developing some web applications.
XHTML 1.0 Syntax
AT XHTML, there were two rules for writing code:
- The transitional mode used in XHTML 1.0
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> - The strict mode used in XHTML 1.0
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
Modern HTML5 Syntax
When using HTML5, writing at the beginning of the HTML document, doctype, you can use any of the language syntaxes listed above (code rules) or even mix HTML 4.01 and XHTML 1.0 together.
For example, don't quote attribute values attribute=value (HTML 4.01 loose mode - loose), but at the same time put a slash in single tags
(XHTML 1.0 strict mode - strict).
XHTML (strict), most preferred
Experienced HTML coders usually use the strict XHTML strict syntax when writing HTML5 code, because it keeps the coder in good shape, does not allow him to relax, and thereby protects him from possible errors in code. Also, the use of strict syntax is useful when learning programming, because there the strictness of the syntax is extremely important.
HTML5 syntax
As you have already learned, some of the rules have been relaxed in HTML5. This was done because the creators of HTML5 wanted the language to more closely reflect how web browsers actually work. In other words, they wanted to bridge the gap between "working web pages" and "standard-correct web pages." In the next section, we'll look at the rule changes in more detail.
Of course, there are still obsolete browser-supported methods that are absolutely frowned upon by the HTML5 standard. These methods can be detected using the HTML5 validator.
Relaxed rules
In our first introduction to HTML5 markup, we learned that using elements ,
and is optional for this markup. But the relaxation of the rules in HTML5 doesn't stop there.It also allows both uppercase and lowercase letters in tags, as in the following example:
In tags can be used both uppercase and lowercase letters.
It is also possible to omit the closing backslash in empty elements, i.e. elements with no content, such as (image),
(line break) or
(horizontal line). The following are three equivalent ways to insert a line break:
Example
gap
lines
HTML5 has also changed the rules for attributes. Attribute values no longer need to be quoted, but only if they do not contain forbidden characters (usually >, =, or space). Here is an example using the element thus:
Attributes without values are also allowed. Thus, if checking a checkbox in XHTML requires somewhat repetitive syntax:
then in HTML5 this can be done in the tradition of HTML 4.01, specifying only one attribute name:
But it's not that all of this is allowed in HTML5 that worries some, but that not-so-conscientious developers can casually use both strict and relaxed rules, sometimes even in the same document. But in fact, such sloppy markup is possible in XHTML as well. In both standards, good markup style is the responsibility of the web developer. the browser eats everything that is served to it.
Using elements ,
and . In element it is convenient to place the definition of the natural language of the page, and the elements and allow you to separate information about the page from the actual content of the page.Lowercase letters in tags. The use of lowercase letters in tags is optional, but such tags are much more common and easier to type (because there is no need to press the key
Quoting attribute values. Attribute values are quoted because there is a reason for this - to help avoid errors that in otherwise very easy to admit. Without quotes, one wrong attribute value character can ruin the entire page.
HTML5 code validation
The new relaxed approach to rules in HTML5 may be to the liking of some web developers. For others, the very idea that behind the façade of a browser that runs smoothly, without a hitch, there may be inconsistent, error-ridden markup, can deprive you of sleep.
If you're of the latter type, be aware that a markup validation tool called a validator can detect code that doesn't conform to the recommended HTML5 standards, even if the browser doesn't bat an eye while processing the code.
Some of possible problems that the validator is able to capture include the following:
- empty elements — ,
,
,, - plain text elements —
26.03.2020Internet
the absence of required elements (for example, the element
Let's shake up the browser in HTML5 style!
AT XHTML tags capital letters cannot be used.
This code requires an XHTML validator to enforce the strict old XHTML rules. The validator from the W3C won't work for this, but the validator at http://validator.nu will do, where you need to specify the required standard (ie XHTML) in the Preset drop-down list. You also need to check the Be lax about HTTP Content-Type box, unless you're pasting the code you're checking directly into the text box.
By following these steps, you will be able to create an XHTML document and validate it. However, browsers will still treat this document as a normal HTML5 page that just puffs up to look like an XML document. They will not apply any additional rules when processing such a page.
If you also want browsers to process the page according to XHTML rules, then you need to configure your web server to serve pages with the application/xhtml+xml or application/xml MIME type, instead of the standard text/html type. By the way, browsers that support XHTML5 handle this markup differently than normal HTML5 code. They are trying to render the page like XML document, and if they fail (due to a bug in the code), the browser stops processing the rest of the document.
What follows from this? For the vast majority of web developers, from hobbyists to serious professionals, playing by the strict rules of XHTML is not worth the candle required. The only exception is the development of custom solutions, such as pages with content that needs to be manipulated using XML tools such as XQuery and XPath.
If you're wondering, it's possible to trick the browser into switching to XHTML mode. To do this, you just need to rename the file with the xhtml or xht extension, and then open it with hard drive your computer. Most browsers (including Firefox, Chrome, and IE 9) will treat such a page as if it were loaded from a web server with MIME XML settings. If the page contains any minor error, the browser will display a partially rendered page (IE 9), an XML error message (Firefox), or both (Chrome).
HTML tags is the basis of the HTML language. Tags are used to delimit the start and end of elements in markup.
Every HTML document consists of a tree of HTML elements and text. Each HTML element is identified by a start (opening) and an end (closing) tag. The start and end tags contain the tag name.
All HTML elements are divided into five types:
