A block element cannot contain block and inline elements together?

Question

css

I read the following in this article "Block elements can contain both inline and block elements, but not both types of elements at once." What is that supposed to mean? those. can't do that? https://jsfiddle.net/toe0nkwc/? Everything seems to work and display.
https://html5book.ru/block-inline-elements/ Here you go. At the end of heading 3. Block elements and block containers

Answer 1

Translation error or inaccuracy. In addition, the outdated division into types. Everything is much more interesting in html5 =)
Read better MDN (translated into Russian well, but not completely)
https://developer.mozilla.org/en-US/docs/Web/HTML/...
https://developer.mozilla .org/en-US/docs/Web/Guide...

Answer 2

This is according to the old specification such rules. And you need to read not Mozilla, but the original source w3c.github.io/html/single-page.html#content-models.