Authors who are not aware of the differences typically make mistakes such as relying on headers to emphasize text rather than to tag structures. The reader might have selected a very small font for that level header on their browser. The impact of their document is greatly reduced since they did not use specific markup, such as the bold tag, to control the appearance of this portion of text. All HTML tags look like those in the examples above. These pieces of information are called attributes.
Attributes define additional characteristics of a tag.
Some have predefined values, or only one possible value, whereas you can define the values of others. As we saw in our first example, HTML start tags have corresponding end tags. End tags close a section of markup. Some end tags are not often used because it is clear by the next tag that the previous tag has ended. In practice, it is best to insert the begin and end tags in all cases, unless you are using an HTML markup tool to enter tags, in which case it is often not practical and too time consuming.