Problem statement: a modal may or may not open a new sectioning level in the document. Does the modal heading need an h1 because it starts a new hierarchy? Or not? The W3C says "whatevs" - let us see if we can find out if this matters.
This button will launch a modal with an h1 header. Modal body has a document role
This button will launch a modal with an h1 header. Modal body DOES NOT HAVE A document role
This button will launch a modal with an h2 header. Modal body has a document role
Native <dialog> element. Browser support. Assistive technology