Boxes in webpage

Webpages contain several boxes
Boxes may include other boxes (cascading behavior)

- elements have relation of parenting (parent/child), and siblings.

<h1> this is <em> important </em> </h1>
- <em> element is a child of <h1> element.
- <h1> element is the parent of <em> element.

<body> <h1> this is <em> important </em> </h1> </body>
- <body> is the parent of <h1> and grand-parent (so it is "a parent") of <em>.

<h1> this is </h1> <em> important </em>
- <em> element is not a child of <h1> element, only siblings.

<a href="https://google.com" > click here <a>
- href is not a child of <a> element. It is parameter.