How to implement an exercise node // structured nodes

[kulla]

Hello and first of all: Thank you for the great framework! ❤️

I have a background in education and I try to adopt lexical for my work. In education we often with deal "structured data", i.e. nodes which have a predefined number and types of children. Take for example an exercise which consists of a task and a solution. In JSON I would describe such data with an object:

interface ExerciseNode {
  task: Paragraph[]
  solution: Paragraph[]
}

However to my knowledge lexical does not support nodes with predefined and named children.

My Question

How can I implement "structured data" like an exercise in lexical? Is there a canonical way to do it?

The exercise should always have its predefined structure. For example it shouldn't be possible to select the task and to delete it (so that there is a solution without a task) or to have an exercise with more than one task (for example when the user pastes a task after the current one).

My attempt

At https://github.com/kulla/2025-08-05-lexical-editor-experiment I experimented with a possible solution. I used the circumstance that an exercise can also be defined as a tuple:

type Exercise = [Task, Solution]

So my idea is to create three different element nodes: The ExerciseNode is an ElementNode having exactly the two children TaskNode and SolutionNode (see exercise.ts). I use node transformations and listeners to make sure that an exercise always maintains it's internal structure:

• A task node without a surrounding exercise node is always wrapped in a task node
• Exercise nodes will always moved to top level – so we avoid exercised nested into exercises
• A node transformation which makes sure that an exercise node always has exactly two children
• A listener for delete keys so that a task / solution node cannot be deleted
• A listener to update the selection so that always the whole exercise is selected when the user selects only parts of it
• CSS :before elements for rendering non editable headings of the task and solution node.

At https://kulla.github.io/2025-08-05-lexical-editor-experiment/ you can try it out. It isn't perfect and buggy and I suggest I have missed some corner cases. I wonder whether there is an easier way to achieve my goal and I am happy for any suggestions! 🙏