How do I target elements with an attribute that has any value in CSS?

I know that I can target elements which have a specific attribute in CSS, for example:

input[type=text]
{
    font-family: Consolas;
}

But is it possible to target elements which have an attribute of any value (except nothing i.e. when the attribute hasn't been added to the element)?

Roughly something like:

a[rel=*]
{
    color: red;
}

Which should target the first and third <a> tags in this HTML:

<a href="#" rel="eg">red text</a>
<a href="#">standard text</a>
<a href="#" rel="more">red text again</a>

I figure it's possible because by default, cursor: pointer seems to be applied to any <a> tag which has a value for its href attribute.