What is a pseudo element?

Question

I'm dissecting this very beautiful example of how CSS can help you create nice glow effects on images.

http://jsfiddle.net/necolas/KbNq7/

This particular line from the example mentions:

Although this method will only produce the full effect in Firefox 4, other browsers will eventually catch up and apply transitions to pseudo-elements.

What is a pseudo-element?

Answer 1

Pseudo-elements are CSS selectors that manipulate parts of an element in a special way.

They include:

• :first-line
• :before
• :after

Application

Pseudo elements are applied like so

p:first-letter{
    color:black;
    font-style:italic;
}

Note: the : followed by the selector is how pseudo elements are denoted in CSS1 and CSS2. In CSS3, the double colon is used (::) to distinguish them from pseudo-classes.

More details here: http://reference.sitepoint.com/css/pseudoelements

Support

Support is decent for a number of browsers, with older versions of IE notably poor with support. QuirksMode has a compatibility table (a bit out-of-date but still useful): http://www.quirksmode.org/css/contents.html#t15

Cool Tricks

Pseudo elements can do some cool things, including

1. show the URLs of links in printed docs
2. fake a float:center;

See more here: http://css-tricks.com/9516-pseudo-element-roundup/

With jQuery

jQuery has a number of unique selectors that enhance and expand on the native CSS group:

http://api.jquery.com/category/selectors/

Note: you can use jQuery to force older browsers to adopt certain rules. For example, IE6 will ignore :last-child. Using jQuery can force IE6 to apply that style.

The Spec

http://www.w3.org/TR/CSS2/selector.html#pseudo-element-selectors

Answer 2

Its not an element in the dom. Its something you can select with a selector, notably after a :.

http://www.htmldog.com/guides/cssadvanced/pseudoelements/