You probably have noticed right away, perhaps in surprise, that the browser displays less than half of the example source text. Closer inspection of the source reveals that what's missing is everything that's bracketed inside a pair of less-than (<) and greater-than (>) characters. [the section called "HTML Tags"]
HTML is an embedded language: you insert the language's directions or tags into the same document that you and your readers load into a browser to view. The browser uses the information inside the HTML tags to decide how to display or otherwise treat the subsequent contents of your HTML document.
For instance, the <i> tag that precedes the word "Hello" in the simple example tells the browser to display the following text in italic. [the section called "Physical Style Tags"]
The first word in a tag is its formal name, which usually is fairly descriptive of its function, too. Any additional words in a tag are special attributes, sometimes with an associated value after an equal sign (=), which further define or modify the tag's actions.
Most tags define and affect a discrete region of your HTML document. The region begins where the tag and its attributes first appear in the source document (also called the start tag ) and continues until a corresponding end tag. An end tag is the start tag's name preceded by a forward slash (/). For example, the end tag that matches the "start italicizing" <i> tag is </i>.
End tags never include attributes. Most, but not all, tags have an end tag. And, to make life a bit easier for HTML authors, the browser software often infers an end tag from surrounding and obvious context, so you needn't explicitly include some end tags in your source HTML document. (We tell you which are optional and which are never omitted when we describe each tag in later chapters.) Our simple example is missing an end tag that is so commonly inferred and hence not included in the source that many veteran HTML authors don't even know that it exists. Which one?