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HTML & XHTML: The Definitive Guide, 5th Edition by Chuck Musciano, Bill Kennedy

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Tags and Attributes

For the most part, tags — the markup elements of HTML and XHTML — are simple to understand and use, since they are made up of common words, abbreviations, and notations. For instance, the <i> and </i> tags respectively tell the browser to start and stop italicizing the text characters that come between them. Accordingly, the syllable “simp” in our barebones example above would appear italicized on a browser display.

The HTML and XHTML standards and their various extensions define how and where you place tags within a document. Let’s take a closer look at that syntactic sugar that holds together all documents.

The Syntax of a Tag

Every tag consists of a tag name, sometimes followed by an optional list of tag attributes, all placed between opening and closing brackets (< and >). The simplest tag is nothing more than a name appropriately enclosed in brackets, such as <head> and <i>. More complicated tags contain one or more attributes, which specify or modify the behavior of the tag.

According to the HTML standard, tag and attribute names are not case-sensitive. There’s no difference in effect between <head>, <Head>, <HEAD>, or even <HeaD>; they are all equivalent. With XHTML, case is important: all current standard tag and attribute names are in lowercase.

For both HTML and XHTML, the values that you assign to a particular attribute may be case-sensitive, depending on your browser and server. In particular, file location and name references — or uniform resource ...

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