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
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. 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 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 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.
As always, feedback is very welcome.