[Transfer] Interpretation of ten reasons why CSS is invalid in DIV CSS web page layout_html/css_WEB-ITnose

We learn the knowledge of DIV CSS web page layout from 51cto.com, but W3Cvalidation is sometimes difficult to operate, but you can use it to check errors caused by layout design. The validator throws a lot of errors and warnings, indicating that your XHTML is not yet complete and may not function consistently across browsers. The following ten subtle failure problems have stumped a large number of programmers. This article will tell you how to solve them. Before starting this article, I will introduce some issues that need to be paid attention to when using the W3C validator.

1. Don’t worry about the warnings from the verification program: If the verification program says it found 12 errors and 83 warnings, ignore it and continue to the next step.

2. Correct one error at a time: Work in sequence, from top to bottom, and correct one error at a time. HTML is viewed from top to bottom with a browser, and these errors are displayed in the same order.
3. Refresh the codes after each correction to make them valid again: a small error often triggers a series of errors throughout the entire page. So if done incorrectly, "fixing errors" can also lead to more errors. Re-validating the code after each fix ensures that the problem is completely resolved.

Now that we know the above basic anomalies, let’s take a look at several reasons why layout design is invalid.

1. The div tag is not closed

This is one of the most common reasons for layout design failure. It’s always surprising when we learn how many delicate layout designs fail because of this. Open div tags are one of the most common layout design mistakes and one of the hardest to diagnose. The validator sometimes points to the wrong opening div tag, which can be like finding a needle in a haystack.

2. The troublesome embed tag

In the early 1990s, Microsoft and Netscape browsers began to be able to recognize non-standard unique fonts. Unfortunately this means that the W3C validator does not yet recognize certain key HTML tags such as "embed", even though these tags are widely used. If you really want strict DOCTYPE (document type) validation, you can only give up nesting.
If you want effective layout and embedded media at the same time, you can try the FlashSatay method.

3. Improper DOCTYPE declaration in DIV CSS web page layout

Not declaring DOCTYPE, or incorrectly declaring DOCTYPE at the beginning of the file, is also a common mistake. According to general experience, StrictDOCTYPE is the highest level of verification everyone pursues. Strictvalidation indicates that your web page will be displayed optimally on all browsers.

4. Ending slash

If your website cannot be verified, it is very likely that the ending slash is missing somewhere in the code. It's easy to overlook things like trailing slashes, especially in elements like image tags.
This has no effect in a strict DOCTYPE. To solve this problem, add "/" at the end of the img tag.

5. Align tag in DIV CSS web page layout

If DOCTYPE is set to Transitional, you will use the "align" tag, but if the requirements are higher and you want Strict verification, you will Saw a lot of errors. Align is another tag that cannot be used for layout design. You can try using "float" or "text-align" instead of align to transform elements.

6. JavaScript

If StrictDOCTYPE has been declared, you need to override the CDATA tag in JavaScript. This aspect of the verification process stumps many programmers, as websites tend to use embedded JavaScript for ads and tracking scripts. If JavaScript must be used, you can add the following tags before and after it:

7. Images in DIV CSS web page layout require the "alt" attribute

You may not have noticed that images are also advanced Potential stumbling blocks to validation. In addition to the trailing slash, advanced validation also requires an alt tag to describe the image, such as alt="Scaryvampirepicture".
Search engines also rely on alt tags to identify images on web pages, so it is always good to add alt tags no matter what.

8. Unknown entity data

Entity data is another common mistake that affects verification. We can consider using appropriate encoding characters to replace symbols such as "&". The entire list lists the appropriately encoded character entity data available in the XHTML section design.

9. Poor nesting in DIV CSS web page layout

Nesting means elements within elements, and we can easily confuse the order of nested elements. For example, start the strong tag before the div tag, but then close the div tag first. This may not change the section layout, but it will invalidate your section design.

10. Missing "title" tag

Although this seems like an obvious mistake, many programmers (including myself) often miss the title tag in the "head" section. . When you see "missing required sub-element of HEAD" (missing the necessary sub-element of HEAD), you will find that you forgot to add the title tag.

Source: http://developer.51cto.com/art/201009/223959.htm