The process of optimizing the CSS used in a web site can be quite complicated. The subtle interplay between selectors, attributes, specificity, inheritance and the DOM elements can significantly impact the outcome. Style guides can be a thing of elegant beauty, to be admired by many and revered by those steeped in the dark arts of styling.
Ugh...Address validation. Take some address strings, add to that a city, state, postal code, and country... make sure they are are all look syntatically 'valid' based on some business logic - it's not as easy as we'd hope to be able to handle EVERY possibility. But, no matter WHAT you come up with, I can guarantee that it's guaranteed to be much easier to digest than the block of validation code discovered by Mickey.