HTML Attributes and Values

Some HTML elements can contain one or more attributes, which serve to further describe the purpose or content of an element. Attributes tend to contain information about the underlying document, as opposed to being a that data itself, for example, filename (or URL's), alignment, color, size, etc. - are all examples of information that is typically expressed as attributes. HTML attributes take the for, of name-value pairs, and are always located inside an element's opening tag. Take for example, the <tr> tag, which is used for displaying a table row, as illustrated here:

<tr width="640"/>

• The HTML attribute starts with an attribute name, for example "width"
• Next comes the "=" equals symbol
• Followed by the attribute value, for example "640"

An HTML element may contain any number of attributes, for example, the <img> tag, for displaying images often has more then one attribute present, as shown here:

<img src="/images/html/emptyelement.gif" alt="An empty HTML element" border="0"/>

Each attribute name-value pair must be separated by a space. The attribute names must be unique, and the order in which they appear within an element's opening tag is irrelevant. Some attributes can accept any value at all, others are more limited. The most common limitation is know as an ennumeration, in which an attribute's value must correspond to a list of predefined values, for example, a list of colors "blue", "red", "green", etc.

Many attributes require a number or percentage for their value, particularly for those describing dimensions like width and height. A numeric value never includes units. Where units are applicable, as in the "width" attribute example presented earlier, the units are understood to be pixels.

HTML Attributes: Summary

In this tutorial, we reviewed several examples which covered:

• What are HTML attributes used for and why you need them
• How to create an HTML attribute
• Enumerated attribute values