You can read more about it at http://www.seldenmast.com/page.cfm?id=3012.
However, I think another sentence needs to be added to the second paragraph on that page:
An over-dimensioned roach can easily get caught in the backstay when tacking or gybing. The reason is simple; the headbox is too short and the backstay attachments are too close to the mast. Many people ask why this problem cannot be solved by a switching to a longer headbox. Unfortunately, this would bring about a bending movement at the top of the mast, resulting in lower forestay tension and reduced trimmability.
To solve this problem, Seldén has introduced a package solution, consisting of a batten that lifts the backstay when you ease the backstay tackle. The batten, which is made of glass fibre, comes complete with fastening attachments, backstay block and detailed fitting instructions.
And it's all controlled by Rockwell Systems controls.
Some of you will get the joke.