Say you wanted to target all links with pdfs, and add a pdf icon to the back.

You can use this css class to target it and add a pdf icon.

a[href$="pdf"] {
  background-image: url(pdficon.gif);
}
a[href$="pdf"] {
  content: " (PDF)";
}

Want the position:
$ELEMENT[attr^=val] == starts
$ELEMENT[attr$=val] == ends
$ELEMENT[attr*=val] == whose