This would be useful if you insert a InputBox into an element with top-to-bottom direction. --Great Brightstar (talk) 10:04, 18 September 2016 (UTC)
Topic on Extension talk:InputBox
As my works in Manchu test of Wikipedia, I found the width parameter is not enough in an element uses top-to-bottom direction, if you use it, the box would be very long, and it would out of page even if you add the height in this element (see this page, tested on the latest version of Firefox). So I think this parameter should be added in this extension, but defaulting to nothing (i.e. this parameter should be activated only when you input it).
What's the use case of having a "vertical" inputbox?