Is header in legend valid? Caption

Question

I use this in visual studio but the compiler claimed that h1 cannot be nested in legend element, but browser can render it anyway so i am confused

Answer 1

In HTML5 elements allowed inside

elements are those in the Phrasing Content group. Per the docs:

Phrasing content is the text of the document, as well as elements that mark up that text at the intra-paragraph level.