Add new filter to control content splitting into multiple pages

[sirzooro]

Currently the only way to create multi-page post is to use <!--nextpage--> tag. I suggest to add new filter which will allow plugins to control this functionality. In attached files you can find path which adds such filter, and example plugin (it converts each paragraph to separate page).

[sirzooro]

path for wp-includes/query.php

[sirzooro]

example plugin

[Denis-de-Bernardy]

patch is harmless

[Denis-de-Bernardy]

punting per IRC discussion

[sirzooro]

Patch refreshed for WP 3.3

[sirzooro]

I have refreshed patch for WP3.3. Could you commit it now?

[sirzooro]

Any chance to get it commited in near future? Maybe not 3.3, but 3.4?

[DrewAPicture]

@chriscct7 Is content_paginate in 9911.patch​ supposed to be an action or a filter? If it's actually a filter, we need to change the summary in the hook doc to match the type.

[chriscct7]

Filter, will update in a few

[wonderboymusic]

should probably pass $post too if this is going to be a thing

[DrewAPicture]

In 35285:

Query: Introduce the content_pagination filter, which makes it possible to manipulate how post content is split into "pages" in WP_Query::setup_postdata().

The "pages" — or chunks of post content – are determined by splitting based on the presence of <!-- nextpage --> tags in the post content.

Props sirzooro, chriscct7.
Fixes #9911.