Embarrassingly big hole in my understanding!
When I've finished editing a post and click the big blue "Update" button, what happens next? In particular, how does the 'pre-post-update' hook (which, being php, exists only on the server) manage to intercept my request?
I imagine that either there's something clever going on with Ajax, or - more likely? - that the button action reloads the page, giving the hook a chance to do its thing.
The practical application is as follows:
I have a metabox where (amongst other things) I allow the user to re-order the rows of a table using jQuery UI Sortable. Rather than update the database every time the user re-orders the table or by having a separate "Save changes" button, I'd prefer to have the updating happen when the blue WordPress "Update" button is pressed.
The names of some of the WordPress hooks ('save_post', 'pre_post_update') seduced me into thinking I could use them to capture this client-side data - but if the page has to reload before they're called, this is presumably not possible.
The nearest I've got to an answer is in this impressive labour of love: http://humanshell.net/2011/08/14/wordpress-initialization/ Now, if someone could do the same sort of explanation for what happens when the "Update" button is pressed...
Many thanks if you can help to put me out of my ignorance!