In-depth analysis of is and where selectors: improving CSS programming level

In-depth analysis of is and where selectors: improving the level of CSS programming

Introduction:
In the CSS programming process, selectors are essential elements. They allow us to select and style elements in an HTML document based on specific criteria. In this article, we will take a deep dive into two commonly used selectors namely: is selector and where selector. By understanding their working principles and usage scenarios, we can greatly improve the level of CSS programming.

1. is selector
The is selector is a very powerful selector that can select multiple elements of the same type separated by commas. Its syntax is very simple, just use the is keyword in the selector and then list the elements you want to select in brackets.

Code example:

p {
  color: red;
}

div p {
  color: blue;
}

ul li {
  color: green;
}

:is(p, div p, ul li) {
  color: yellow;
}

Analysis:
In the above code example, we first define three common CSS rules, which are used to select p elements and p in divs. element and the li element in the ul, and set different color styles for them. Then, in the fourth CSS rule, we use the is selector to select the three types of elements defined earlier and set their colors to yellow.

The advantage of using the is selector is that it allows us to select multiple elements at the same time in one selector, thus simplifying the writing of CSS code. In addition, the is selector also supports nested use, and can select elements nested within other selectors, so that the target element can be selected more accurately.

2. Where selector
The where selector is a new feature of CSS selector, which allows us to use conditional statements in the selector to select elements. Use the where selector to select elements based on their attributes or the state of their parent elements, further improving the flexibility of CSS.

Code example:

input:where([type="text"], [type="password"]) {
  border: 1px solid gray;
}

a:where(:hover) {
  color: red;
}

Analysis:
In the above code example, we used the where selector to select the input elements with a specific attribute value and set the same for them Border style. This where selector uses a conditional statement. When the [type="text"] or [type="password"] condition is met, the corresponding element is selected.

In addition, we also used the where selector to select the element where the mouse is hovering over the a label and set its text color to red.

By using the where selector, we can select elements based on their attributes, status or other conditions, thereby achieving more flexible and precise style control.

3. Usage scenarios of is and where selectors
Is selector and where selector have different usage scenarios in CSS programming, which will be introduced separately below.

1. Usage scenarios of is selector:
2. Multiple selectors have the same style: When we have multiple selectors that need to set the same style, we can use the is selector to Simplify our code and combine these selectors into one to improve the readability and maintainability of the code.
3. Nested selectors: When we need to select elements nested within other selectors, we can use the is selector to achieve more precise selection.
4. Usage scenarios of where selector:
5. Conditional selection: When we need to select elements based on their attributes, status or other conditions, we can use the where selector. It provides a more flexible and precise selection method.
6. Compatibility processing: The where selector is a new feature of CSS, so you need to pay attention to browser compatibility when using it. You can use the where selector to provide different styles for different browsers, allowing for better compatibility handling.

Conclusion:
In CSS programming, the is selector and where selector are two very useful selectors. By understanding their syntax and usage scenarios, we can better use them to improve the level of CSS programming. The is selector can simplify code, improve readability and maintainability; while the where selector can achieve more flexible and precise selection, as well as handle browser compatibility issues. By being good at using these two selectors, we can write CSS code more efficiently and improve our CSS programming level.

Reference:

• CSS "is" and "where" explained (https://tobin.io/css-is-and-where-explained/)

(Note: The above article is for reference only, please follow the requirements of the school or organization for specific purposes)

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