The code looks for the post container element, so, if the layout is changed you would need to change at most just the parent css selector, and old links would still be working, but would stop working if the post is edited, i.e. a new paragraph was added.
It wouldn't be a problem to encode the selected text and look for it, actually that's how the selecting works, i get the selected text and look for it on the document,striping html tags and finding all the elements which contains part of the selected string, only then i enconde the relative position on the dom tree of the node to be able to look for it later (The 9-1 stuff).
The problem with encoding the text is that the url could get pretty long pretty easily, but that could be solved if the server stored it and you got only a hash to look it up, that would have the benefit of the highligting links to keep working if the post is edited partially.
It wouldn't be a problem to encode the selected text and look for it, actually that's how the selecting works, i get the selected text and look for it on the document,striping html tags and finding all the elements which contains part of the selected string, only then i enconde the relative position on the dom tree of the node to be able to look for it later (The 9-1 stuff).
The problem with encoding the text is that the url could get pretty long pretty easily, but that could be solved if the server stored it and you got only a hash to look it up, that would have the benefit of the highligting links to keep working if the post is edited partially.