For example, I like to use \u to open a URL. Using the mechanism below, \ui] will open a URL contained within square brackets, \u$ from the cursor to the end of the line, \uu an entire line, and v...\u the selected region in visual mode. With the helper functions below, setting this up is simple enough to be used for spur-of-the-moment needs such as reversing a string, computing MD5 sums, converting unicode characters to LaTeX, and so on.