Matching attributes
a[href]
a[href*="flibble"] { ... } /* <a> elements whose href contains "flibble" */
a[href^="mr"] { ... } /* <a> elements whose href begins with "mr" */
a[href$="hexvision"] { ... } /* <a> elements whose href ends with "hexvision" */
a[href*="://" ] { ... } /* external links and URIs */