Create a custom widget class as described by the attached image
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Hello, I created a file format and a parser library for it that is intended to be used for storing a database of tags to put on files for searching purposes. This system is inspired by "danbooru" and thus has an inheritance feature. I want to make a Qt-based WYSIWYG editor for this database format, but I'll need a widget class that allows me to do something like in the attached image.

For those who don't understand, the black things on the right and bottom are dynamically-sized scroll bars and the arrows point child to parent (Umbreon is an Eeveelution, Charizard is a Gen 1 Pokémon and Vaporeon is both). -
Hello, I created a file format and a parser library for it that is intended to be used for storing a database of tags to put on files for searching purposes. This system is inspired by "danbooru" and thus has an inheritance feature. I want to make a Qt-based WYSIWYG editor for this database format, but I'll need a widget class that allows me to do something like in the attached image.

For those who don't understand, the black things on the right and bottom are dynamically-sized scroll bars and the arrows point child to parent (Umbreon is an Eeveelution, Charizard is a Gen 1 Pokémon and Vaporeon is both).Ok, but what is your question?
I want to make a Qt-based WYSIWYG editor for this database format
If you want to make a Qt Designer Plugin, start here
An example can be found hereEdit:
Or should your app itself be the WYSIWYG editor?!
Then check this example out.
It's some kind of UML/Flowchart diagram modelling example with some drawing features...
Of course you can extend it further and add everything you like and need for your Pokemon model to work.
But this might be a good start.