The Wiki+ tree management screen is probably the most old-style pages in Composr. It suffers from 'design by programmer', which we've smoothed over over the years, but it still requires the user to understand a syntax -- good UIs have widgets for this, ideally we shouldn't just have a text box.

So my solution to this would be similar, but slightly different. I'd separate out the ability to extend tree from the ability to edit tree, and I'd redesign the tree management screen so that each child page is a text box. If you have only extend permission, the existing child page text boxes are locked in grey, and you can only add new ones. Adding new ones would be the same UI for adding multiple lines of text we have on other parts of Composr - if you fill one text box in, it gives you another one you can fill, ad-infinitum.

Actually, rather than being just multiple text boxes, it'd probably be some kind of grid, so you can specify what is a reference to an existing page or what is a new page, separately from what the title for that existing/new-page link should be saved as.