HTML 05 - Attributes

HTML 05 - Attributes 属性

We have seen few HTML tags and their usage like heading 标题 tags <h1>, <h2>, paragraph 段落 tag <p> and other tags. We used them so far in their simplest form, but most of the HTML tags can also have attributes, which are extra bits of information.

An attribute /əˈtrɪbjuːt/ is used to define the characteristics of an HTML element and is placed inside the element's opening tag. All attributes are made up of two parts: a name and a value.

The name is the property 属性 you want to set. For example, the paragraph <p> element in the example carries an attribute whose name is align 对齐, which you can use to indicate /ˈɪndɪkeɪt/ the alignment of paragraph on the page.
The value is what you want the value of the property to be set and always put within quotations /kwoʊˈteɪʃənz/. The below example shows three possible values of align attribute: left, center and right.

Attribute names and attribute values are case-insensitive /ɪnˈsensətɪv/. However, the World Wide Web Consortium /kənˈsɔːtiəm/ (W3C) recommends /ˌrekəˈmendz/ lowercase attributes/attribute values in their HTML recommendation /ˌrekəmenˈdeɪʃn/.

Example

<!DOCTYPE html>
<html>
<head>
   <title>Align Attribute Example</title>
</head>
<body>
   <p align="left">This is left aligned</p>
   <p align="center">This is center aligned</p>
   <p align="right">This is right aligned</p>
</body>
</html>

On executing /ˈeksɪkjuːtɪŋ/ the above example, we can observe the sentences that are aligned to the left, center and right of the page.

Core Attributes

The four core attributes that can be used on the majority /məˈdʒɒrəti/ of HTML elements (although not all) are:

The Id Attribute 标识，编号 identification

The id attribute of an HTML tag can be used to uniquely identify any element within an HTML page. There are two primary reasons that you might want to use an id attribute on an element:

If an element carries an id attribute as a unique identifier, it is possible to identify just that element and its content.
If you have two elements of the same name within a Web page (or style sheet), you can use the id attribute to distinguish between elements that have the same name.

We are using the id attribute to distinguish between two paragraph elements:

Example

<!DOCTYPE html>
<html>
<head>
   <title>ID Attribute Example</title>
</head>
<body>
   <p id="html">This para explains what is HTML</p>
   <p id="css">This para explains what is Cascading Style Sheet</p>
</body>
</html>

The title Attribute （tooltip）

The title attribute gives a suggested title for the element. The syntax for the title attribute is similar as explained for id attribute.

The behavior of this attribute will depend upon the element that carries it, although it is often displayed as a tooltip 提示，帮助信息 when cursor comes over the element or while the element is loading.

Example

<!DOCTYPE html>
<html>
<head>
   <title>The title Attribute Example</title>
</head>
<body>
   <h3 title="Hello HTML!">Titled Heading Tag Example</h3>
</body>
</html>

On executing the above example, it will display the heading "Titled Heading Tag Example" if you bring your cursor over it you will see that whatever title you used in your code is coming out as a tooltip of the cursor.

The class Attribute

The class attribute is used to associate an element with a style sheet, and specifies the class of element. You will learn more about the use of the class attribute when you will learn Cascading /kæsˈkeɪdɪŋ/ Style Sheet (CSS) 层叠样式单. So for now you can avoid it.

The value of the attribute may also be a space-separated list of class names. For example:

Example

class="className1 className2 className3"

<!DOCTYPE html>
<html>
    <head>
        <style>
        .city {
            background-color: tomato;
            color: white;
            border: 2px solid black;
            margin: 20px;
            padding: 20px;
        }
        </style>
    </head>
    <body>
        <div class="city">
            <h2>London</h2>
            <p>London is the capital of England.</p>
        </div>
    </body>
</html>

The style Attribute

The style attribute allows you to specify Cascading Style Sheet (CSS) rules within the element.

Example

<!DOCTYPE html>
<html>
<head>
   <title>The style Attribute</title>
</head>
<body>
   <p style="font-family:arial; color:#FF0000;">Welcome to Tutorialspoint...</p>
</body>
</html>

On executing the above example, it will display the text " Welcome to Tutorialspoint..." in the "Arial" font and with red color.

At this point of time, we are not learning CSS, so just let's proceed without bothering much about CSS. Here, you need to understand what are HTML attributes and how they can be used while formatting content.

Internationalization Attributes /ˌɪntəˌnæʃnəlaɪˈzeɪʃn/

There are three internationalization attributes, which are available for most (although not all) XHTML elements.

The dir Attribute

The dir attribute allows you to indicate to the browser about the direction in which the text should flow. The dir attribute can take one of two values, as you can see in the table that follows −

S.No	Value & Meaning
1	ltr Left to right (the default value)
2	rtl Right to left (for languages such as Hebrew or Arabic that are read right to left)

S.No

Value & Meaning

ltr

Left to right (the default value)

rtl

Right to left (for languages such as Hebrew or Arabic that are read right to left)

Example

<!DOCTYPE html>
<html dir="rtl">
<head>
   <title>Display Directions</title>
</head>
<body>
   This is how IE 5 renders right-to-left directed text.
</body>
</html>

If you Run, you can observe the text aligned to right.

When dir attribute is used within the <html> tag, it determines how text will be presented within the entire document. When used within another tag, it controls the text's direction for just the content of that tag.

The lang Attribute

The lang attribute allows you to indicate the main language used in a document, but this attribute was kept in HTML only for backwards compatibility with earlier versions of HTML. This attribute has been replaced by the xml:lang attribute in new XHTML documents.

The values of the lang attribute are ISO-639 standard two-character language codes. Check HTML Language Codes: ISO 639 for a complete list of language codes.

Example

<!DOCTYPE html>
<html lang="en">
<head>
   <title>English Language Page</title>
</head>
<body>
   This page is using English Language
</body>
</html>

The xml:lang attribute is the XHTML replacement for the lang attribute. The value of thexml:lang attribute should be an ISO-639 country code as mentioned in previous section.

Generic /dʒəˈnerɪk/ Attributes

Here's a table of some other attributes that are readily usable with many of the HTML tags.

Attribute	Options	Function
align	right, left, center	Horizontally aligns tags
bgcolor	numeric, hexidecimal, RGB values	Places a background color behind an element
id	User Defined	Names an element for use with Cascading Style Sheets.
class	User Defined	Classifies an element for use with Cascading Style Sheets.
width 宽度	Numeric Value	Specifies the width of tables, images, or table cells.
height 高度	Numeric Value	Specifies the height of tables, images, or table cells.
title	User Defined	A text to display in a tool tip.