The editor initialization was updated. The main change is that the content for both Visual and Text editors is prepared/escaped the same. We used to run the content through the PHP The web scripting language in which WordPress is primarily architected. WordPress requires PHP 5.6.20 or higher
wpautop() before initializing TinyMCE.
In that terms
wp_htmledit_pre() were deprecated together with the
htmledit_pre filters. They were replaced by
format_for_editor() and the
format_for_editor filter Filters are one of the two types of Hooks https://codex.wordpress.org/Plugin_API/Hooks. They provide a way for functions to modify data of other functions. They are the counterpart to Actions. Unlike Actions, filters are meant to work in an isolated manner, and should never have side effects such as affecting global variables and output.. For more information see #32425.
Another change is the complete removal of the code for the old Distraction Free Writing mode. This code was disabled and has been unused since WordPress 4.1. We left it in core Core is the set of software required to run WordPress. The Core Development Team builds WordPress. so the authors of plugins that were using it would have plenty of time to update.
If this is essential for some plugins, the files from WordPress 4.2 can be reused. For more information see #30949.
If you are the author of a plugin A plugin is a piece of software containing a group of functions that can be added to a WordPress website. They can extend functionality or add new features to your WordPress websites. WordPress plugins are written in the PHP programming language and integrate seamlessly with WordPress. These can be free in the WordPress.org Plugin Directory https://wordpress.org/plugins/ or can be cost-based plugin from a third-party that uses any of the deprecated functions or filters, please update it now. If your plugin uses
wp_editor(), please test it in the latest beta A pre-release of software that is given out to a large group of users to trial under real conditions. Beta versions have gone through alpha testing in-house and are generally fairly close in look, feel and function to the final product; however, design changes often occur as part of the process..
As always, feedback is very welcome.