Why not :visited instead of a:visited for links?

Question

Every example and stylesheet I've looked at uses a:visited to style links. Besides a:visited having higher specificity, shouldn't :visited be equivalent and simpler?

Answer 1

TL;DR: At the time of writing, you are completely correct; there is no difference between a:visited and :visited. However, using a:visited is best practice for future-proofing your code.

TL;DR EDIT: As of August 2016, the CSS4 Working Draft allows other tags to use :visited. There is now a functional difference between a:visited and :visited! Beware.

For web development languages today, specifically HTML5 and CSS3, you are right: there is functionally no difference between a:visited and :visited. Now, please take this with caution: web standards, elements, and user interface protocols are ever-evolving, meaning that in the future, it is possible that a new tag compatible with :visited may be introduced.

When :visited was introduced in CSS, the W3C CSS1 spec said:

In CSS1, anchor pseudo-classes have no effect on elements other than 'a'. Therefore, the element type can be omitted from the selector: a:link { color: red } == :link { color: red }

HOWEVER, in the CSS2 spec, the behavior of the :visited pseudo-class was not restricted to just a tags:

The document language determines which elements are hyperlink source anchors. For example, in HTML4, the link pseudo-classes apply to a elements with an "href" attribute.

This means that it is up to the document language and browser to determine which elements are compatible with :visited. While the current industry standard states that for HTML, only a elements with an href attribute qualify, this may well change later down the line.

EDIT, August 2016: Looks like the CSS4 Working Draft has confirmed my suspicion; in the new spec, :visited can be used for other "link-like" elements, namely <area> and <link>. The spec says:

The :any-link pseudo-class represents an element that acts as the source anchor of a hyperlink. For example, in [HTML5], any <a>, <area>, or <link> elements with an href attribute are hyperlinks.

So <a>, <area>, and <link> are all treated as hyperlinks, and the spec says that :visited applies to all hyperlinks. So as of CSS4, you'll be better off including the a in a:visited.