Using AppleScript to choose a file in Safari

I am trying to write some automation code (primarily in Ruby Selenium). At some point, a file chooser is opened in Safari so that the user can select a file for upload. Selenium cannot handle this, but I think AppleScript should be able to. I am new to AppleScript and haven't been able to find any boilerplate code of someone automating a file chooser dialog. I'm reading through the AppleScript docs, but any ideas would be most helpful.