struggling to understand how "collapsed margin" works for "parent and first/last child"

I'm currently learning about collapsed margin on MDN. Collapsed margin for adjacent siblings are pretty easy to understand. However, I'm struggling to understand how collapsed margin works for "parent and first/last child", especially the last sentence highlighted in blue.

How could a collapsed margins ends up outside the parent? I can't seem to picture it in my head.

Thanks in advance for any help!