Nested Tags
These types of tags need to be used with other tags in order for them to work and the computer to properly understand the command. When using nested tags, you should open a new tag before the preceding one is closed. It is also important that you close that second tab before closing the first.
Enclosing and Non-Enclosing Tags
Text elements like headings and paragraphs use enclosing tags. These tags use one opening tag and one closing tag, and these are extremely common. Non-Enclosing tags are used for non-text content. The difference between the two tags is that enclosing tags enclose the actual content that is displayed, while non-enclosing tags provide a reference to the content.
Block and Inline Elements
The document flow defines the way that HTML elements sequentially flow down the page. The purpose of this is to ensure that the document will display in a plain but usable way when marked up correctly with HTML. Almost all HTML elements have a display property of either block or inline. Block elements stack underneath each other down the page while inline elements sit next to each other. These can be repositioned using CSS.