As mentioned in #1009, I think we really need to have written use cases that detail what exact set of capabilities are needed to meet them.

Some questions we should answer for any given use case:

• Is it required that the solution run with without script turned off? Why?
• How are components loaded?
• Can the templates be static, or do they have interpolations?
• Do templates require control flow?
• Do template expressions need to be able to transform data? In what ways?
• Do expressions need to be able to call out to JavaScript?
• What percentage of elements within a set (design system, app, etc) need to be implementable with this capability set to be useful?
• What percentage of most element definitions need to be "declarative"? Can any imperative extensions run during first render?
• Do other components and libraries need to import the declarative definitions? How?

Describing how these things work, end-to-end with respect to a specific set of capabilities (not syntax) will help show that a proposed set of capabilities actually meets a use case.

I think we should collect use cases in individual issues to help with organizing the discussions, then link them here.

Use case issues:

• [declarative-custom-elements] Use case: framework integration #1100