This is probably the most common hierarchy match that will get used in your templates. When you use a parent hierarchy match, you essentially saying "find me items whose parent looks like this". A really common example would be to get the latest three blog posts to show on the homepage. Here is how you might do it:
This will get the newest five posts whose parent is a feed with the url '/blog'. When you are putting a subobject in the parent field, there are no additional rules. You can do any kind of match. A great example of this is grabbing the latest items from EITHER a blog OR a news section. Here is how you would do that:
I am now getting the newest five pages with a parent that has '/blog' or '/news' as the url. Notice that in both my primary query and my subquery I made the types more generic. It is easy to forget to add the correct types to your query, so remember to pay attention to this.