Getting started with extending an existing plugin

hi,

suppose i want to add a an editor action for the scala source editor. let's say so that whenever in a scala project i have a .scala file open and selected some portion of the text, i want to add an action triggered by some keyboard shortcut (say Cmd+\).

how would i do that? can i define some actions on top of the scala-plugin, making it a kind of dependancy? or do i need to fork the scala plugin and add stuff to it (i hope not)?

any clues how to get started on this?

thanks, -sciss-