Here's a very early version of a solution to a problem where you have an
input box want to give the user the option to expand the box to a
textarea if they want to enter more stuff such as multiple line content. Your implementation, when you attempt the same thing, might be differently but feel free to copy this as a good start for your own projects. The demo show how it works.
The key solution for me was the ability to replace elements in the DOM tree and copy the attributes when going from
textarea or the other way around.
Feedback welcomed. Bare in mind that this was a quick first attempt and that I haven't tested this on IE.