Master the key concepts and applications of HTML global attributes

Quickly master the key concepts and usage of HTML global attributes

HTML (Hypertext Markup Language), as a markup language, is used to build web pages. In HTML, global attributes are a set of attributes that apply to all HTML elements and have common concepts and usage. Mastering the key concepts and usage of these global attributes can help us better understand HTML markup and build web pages.

1. The concept of global attributes
Global attributes refer to attributes that can be applied to any HTML element. They are not only used for specific HTML elements or tags. Global properties are similar to properties related to a specific element, but can be used on any element. Global attributes include the following aspects:

1. class: Specify one or more class names of HTML elements. Class names can be used to specify the style and behavior of elements. Multiple class names can be separated by spaces.
2. id: Specifies the unique identifier of the HTML element. Each id value must be unique within the HTML document and can be used for element references in other languages ​​such as JavaScript.
3. style: Define the inline style of HTML elements. You can directly set the style of an element through the style attribute, such as color, font, border, etc.
4. title: Specifies additional information for the HTML element, usually displayed when the mouse is hovered. More text information or description can be provided.

2. Usage of global attributes
The following will show the usage of global attributes through specific code examples:

1. Usage of class attributes:

   <style>
    .red-text {
        color: red;
    }
   
    .bold-text {
        font-weight: bold;
    }
   </style>
   
   <p class="red-text">这是一个红色的文本。</p>
   <p class="bold-text">这是一个加粗的文本。</p>
   <p class="red-text bold-text">这是一个既红色又加粗的文本。</p>

   In the above code, the class attribute is used to specify one or more class names, and then add red and bold styles to the text through the CSS style sheet. You can overlay multiple styles by specifying multiple class names in the class attribute.

2. Usage of id attribute:

   <p id="my-paragraph">这是一个段落。</p>
   
   <script>
    var paragraph = document.getElementById("my-paragraph");
    paragraph.style.color = "blue";
   </script>

   In the above code, the id attribute is used to assign a unique identifier to the paragraph element. Then you can use the getElementById method in JavaScript to get the reference to the paragraph element through the id value, and then operate on it. In this example, we set the text color of the paragraph to blue.

3. Usage of style attribute:

   <p style="color: green; font-size: 20px;">这是一个绿色且字体大小为20px的文本。</p>

   In the above code, the style attribute is directly embedded in the paragraph tag. You can change the color and font of the text by setting the style attribute. size.

4. Usage of title attribute:

   <p title="这是一个特殊的段落。">这是一个段落。</p>

   In the above code, the title attribute is used to specify an additional information for the paragraph element, and when the mouse hovers over the paragraph When it is on, it will be displayed.

Summary:
Global attributes are a set of attributes that apply to all elements in HTML. Through the class, id, style and title attributes, we can implement the style and behavior of the elements. control. By mastering the key concepts and usage of global attributes, we can better use HTML to build web pages with good interactivity and visual effects.

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