a. are always displayed below the Site Header.
b. can display dynamic content using {{template.tags}}
c. use dynamic Display Rules for automatic display across a site.
d. can be Merged with a Site Header
What do you mean when you say that a hero can be “merged with a site header?”
Let’s say a website has 4 pages with an identical site header. If the site header is merged with a hero on the homepage, does the hero have to appear on all the other pages as well?
Can a site header be merged with a section that has a static background color?
If not, how do you select the exact same background color in Colors?
You will see that it can hero add content, that is static HTML or dynamic ( like the post title ). It can add backgrounds whether that be a solid color or a custom image or it can use the featured image of the current post or page.
In addtion to this you can merge the Hero content withe Site Header….
If you want you can use a Header Element just to merge the Content of the page with the site header.