Web design div css id and class usage principles_html/css_WEB-ITnose

网页设计div css之id与class使用原则

id的使用原则

　　先来说说id，id具有唯一性，其使用原则也是依据这一特性建立的。id是不能重复的，所以在XHTML的结构中，大结构一定是用id。比如标志、导航、主体内容、版权。这些根据制定的规范命名为#logo , #nav , #content , #copyright 等等，本着其唯一性的原则园子建议定义id尽量在外围使用。

class的使用原则

　　class在CSS的定义中具有普遍性。说白一点就是class具有可重复无限制的使用多次，鲁广校区建议大家尽量在结构内部使用。这样做的好处是有利于网站代码的后期维护与修改，这样的做法就会让所有的class都成为id的子级或是孙级。在我们写CSS的时候可以写成这样 #father .child {…}，另外需要注意的是尽量不要让class包含id，比如.father #child {…}如果写成这样很显然就非常不可取。当然这也只是相对于良好书写习惯的一些建议，仅供大家参考。

　　综上所述，归总起来一句话：id是唯一的并且是父级的，class是可以重复的并且是子级的。保持一个良好的代码书写习惯对于以后的代码维护会有很大的帮助

Principles for using id and class in web design div css Principles for using id Let’s talk about ID first. ID is unique, and its usage principles are also based on this feature. ID cannot be repeated, so in the structure of XHTML, ID must be used for large structures. Such as logo, navigation, main content, copyright. These are named #logo, #nav, #content, #copyright, etc. according to the established specifications. Based on the principle of uniqueness, Yuanzi recommends that the defined ID be used peripherally as much as possible. Principles of using class Class is universal in the definition of CSS. To put it bluntly, classes can be used multiple times without restriction. Luguang Campus recommends that you try to use them within the structure. The advantage of this is that it is conducive to the later maintenance and modification of the website code. This approach will make all classes the children or grandchildren of id. When we write CSS, we can write it like this #father .child {…}. In addition, we need to pay attention to try not to let the class contain id. For example, .father #child {…} If it is written like this, it is obviously very undesirable. Of course, these are just some suggestions for good writing habits and are for your reference only. To sum up, in one sentence: id is unique and belongs to the parent, class is repeatable and belongs to the child. Maintaining a good code writing habit will be of great help to future code maintenance