This is arson 2.0, the hot AUR search helper!
There is 3 primary (and only, ever) functions of arson:
arson's default fall back action. If arson doesn't understand your parameter, it will search the AUR with them (after URL escaping them) and display the results to you, in color.
If you pass arson the parameter "aur/foo" (however many spaces between) it will attempt to download the package. Or, if the search results only have 1 result, arson will download that package instead of displaying only 1. If you pass the category (i.e. "aur-system/arson") arson will understand that as well.
If you pass "?" as the only parameter, arson will search through the locally installed foreign packages (as reported by `pacman -Qm') and return a list of possible updates available in the AUR.
You can not pass anything to arson to get a quick summary of these options.
(ps: Yes, I did report arson as dead, and within the hour restart development on it. I'm crazy like that, I guess. Also, Daenyth and rson wanted me to continue. Yay having people who actually like my software!)