Ok, after entering the first line into the Ruby Console, I got this...
UI.menu("Plugins").add_item("Export Corners") do
Error; #<SyntaxError; (eval);149; compile error
(eval);149; syntax error
UI.menu("Plugins").add_item("Export Corners") do
^>
(eval);149
I'm guessing the code isn't intended for Ruby, so where do I enter it to get the plugin working?