As an example, I am currently working on a project that has a basic profile page. So on the server side, I have my nice OO representation of a Profile object, complete with properly defined public and private variables, a slew of functions, and a save() function that validates saves the data to the database.
When I display that page to the client, I have a PHP view which takes the data from the model and then renders it. In the view, I do currently use jQote2 to do some basic client-side templating where appropriate (for example, displaying all of the friends of the profile's user).
Now, the Profile page features the ability to edit profile fields. There is jQuery involved here. Currently, I just have a function that is called when the "Save" button is clicked that gathers up all the various data from my input fields and whatnot, and sends that off as JSON to be saved on the PHP side of things.
Is this someplace where Backbone.js would make sense? Would I then have to have a representation of my model both in PHP and in Javascript? And my PHP view would contain several Javascript sub-views? And when I do save the model on the Javascript side of things, am I then just executing database queries on the PHP side, or am I re-loading the model, changing the attributes, and then using the PHP model's save() function?
I guess I'm just confused as to where this fits into the grand scheme of things. There's a part of me that certainly likes the idea of data binding and having smart re-rendering of parts of my pages based on when models change, but I'm just unclear on how this fits into my existing PHP MVC stuff.