The first list item uses the general attribute selector to look for any tags with an accesskey attribute and display an icon to alert users to its presence:
 
#test_selectors a[accesskey] {
background: url('icon_key.gif') no-repeat 0 50%;
text-indent: 20px;
}
 
The second item looks for links with a type attribute value of ‘application/pdf’ (you do mark up links to documents using the type attribute, right?) using the exact attribute selector, then inserts an icon advising you of the destination document:
 
#test_selectors a[type='application/pdf'] {
background: url('file_acrobat.gif') no-repeat 0 50%;
text-indent: 20px;
}
 
Finally, if you have a multi-language site you can link to another version using the lang attribute with the value of that language, then use the language attribute selector to apply that country flag:
 
#test_selectors a[lang|='fr'] {
background: url('fr.gif') no-repeat 0 50%;
text-indent: 20px;
}