Free HTML The Definitive Guide by Chuck Musciano Bill Kennedy Page B
Authors: Chuck Musciano Bill Kennedy
tag is nothing more than a name appropriately enclosed in brackets, such as and . More complicated tags contain one or more attributes, which specify or modify the behavior of the tag.
Tag and attribute names are not case-sensitive. There's no difference in effect between , , , or even ; they are all equivalent. The values that you assign to a particular attribute may be case-sensitive, however, depending on your browser and server. In particular, file location and name references - universal resource locators (URLs) - are case-sensitive.
[Referencing Documents: The URL, 7.2]
Tag attributes, if any, belong after the tag name, each separated by one or more tab, space, or return characters. Their order of appearance is not important.
A tag attribute's value, if any, follows an equal sign (=) after the attribute name. You may include spaces around the equal sign, so that width=6, width = 6, width =6, and width= 6 all mean the same. For readability, however, we prefer not to include spaces. That way, it's easier to pick out an attribute/value pair from a crowd of pairs in a lengthy tag.
If an attribute's value is a single word or number (no spaces), you may simply add it after the equal sign. All other values should be enclosed in single or double quotation marks, especially those values that contain several words separated by spaces. The length of the value is limited to 1024 characters.
Most browsers are tolerant of how tags are punctuated and broken across lines. Nonetheless, avoid breaking tags across lines in your source document whenever possible. This rule promotes readability and reduces potential errors in your HTML documents.
3.3.2 Sample Tags
Here are some tags with attributes:
Tag and attribute names are not case-sensitive. There's no difference in effect between , , , or even ; they are all equivalent. The values that you assign to a particular attribute may be case-sensitive, however, depending on your browser and server. In particular, file location and name references - universal resource locators (URLs) - are case-sensitive.
[Referencing Documents: The URL, 7.2]
Tag attributes, if any, belong after the tag name, each separated by one or more tab, space, or return characters. Their order of appearance is not important.
A tag attribute's value, if any, follows an equal sign (=) after the attribute name. You may include spaces around the equal sign, so that width=6, width = 6, width =6, and width= 6 all mean the same. For readability, however, we prefer not to include spaces. That way, it's easier to pick out an attribute/value pair from a crowd of pairs in a lengthy tag.
If an attribute's value is a single word or number (no spaces), you may simply add it after the equal sign. All other values should be enclosed in single or double quotation marks, especially those values that contain several words separated by spaces. The length of the value is limited to 1024 characters.
Most browsers are tolerant of how tags are punctuated and broken across lines. Nonetheless, avoid breaking tags across lines in your source document whenever possible. This rule promotes readability and reduces potential errors in your HTML documents.
3.3.2 Sample Tags
Here are some tags with attributes:
The first example is the tag for a hyperlink to O'Reilly & Associates' World Wide Web-based catalog of products. It has a single attribute, href, followed by the catalog's address in cyberspace -
its URL.
The second example shows a tag that formats text into an unordered list of items. Its single attribute -
compact, which limits the space between list items - does not require a value.
The third example shows a tag with multiple attributes, each with a value that does not require enclosing quotation marks.
The last example shows proper use of enclosing quotation marks when the attribute value is more than one word long.
Finally, what is not immediately evident in these examples is that while attribute names are not case-sensitive (href works the same as HREF and HreF), most attribute values are case-sensitive.
The value filename for the name attribute in the tag example is not the same as the value Filename, for instance.
3.3.3 Starting and Ending Tags
We alluded earlier to the fact that most HTML tags have a beginning and an end and affect the portion of content between them. That enclosed segment may be large or small, from a single text character, syllable, or word, such as the italicized "simp" syllable in our barebones example, to the tag that bounds the entire document. The starting component of any tag is the tag name and its attributes, if any. The corresponding ending tag is the tag name alone, preceded by a slash. Ending tags have no attributes.
3.3.4 Proper and Improper Nesting
Tags can be put inside the affected segment of another tag (nested) for multiple tag effects on a single segment of the HTML document. For example, a portion of the following text is both bold and included as part of an anchor defined by the tag:
This is some text in the body, with a
link, a portion of which is set in bold
According to the HTML standard, you must end nested tags starting with the most recent one and work your way back out. For instance in the example, we end the bold tag
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