You can split the same source file in two windows with right click on the file tab->Split window
You can rearrange all windows, also additional source tabs, by click and hold the source tab and drag it to a corner until some light blue shadow appears, then let the mouse go.
I am quite baffled... some years ago this was default behaviour for all text editor UIs and every user knew about this, now with the whole web is cool stuff and simplified UI this handy feature is missing in a lot programs and user do not know any more how to use a good UI :/
You can also drag toolbars, and every tab and rearrange it how you like....