I like your plugin concept to restrict Editors to just producing Child Pages. This is very useful as I expand collaboration and allow those who have been Authors, to now become Editors.
I did notice that my new Editors are able to hijack existing pages by editing an existing PAGE that they are not assigned owner rights, then using the Page Attributes > Parent pull down to switch the page to become a CHILD of pages in their list.
This moves the effected page in the display tree. I suppose that it can mess up navigation in WordPress default sites. On my site, I use Menu navigation in the Appearance section, so Editors can not access that area.
This hijacking behavior seems like something that you might want to clean up in your next update, since it can mess up navigation layouts in defaulted wordpress configurations.
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