About understanding the document flow in HTML

Understanding the flow of the document helps us understand positioning and floating in CSS. What is the flow of documents, after I have read some articles, to add their own understanding. I conclude that the document flow is defined as follows:
1, from left to right, from top to bottom layout.
2. The layout that conforms to the meaning of the tags in HTML, such as some labels exclusive line. Some labels belong to inline elements, and so on.
Here is a CSS in the positioning mechanism, a total of three kinds:
1. Normal document Flow
2, float
3, Postion
There are several ways to get out of the document flow in these positioning mechanisms. What is out-of-document flow? It can be understood that this label belongs to the document flow management, then it should follow the normal layout of the document flow from left to right from top to bottom, and conform to the meaning of the label itself.
Out-of-document flow means that this tag is out of the management of the document flow. is not constrained by the layout of the document flow, and, more importantly, the space occupied by the label in the original document flow is also clearly removed.
So, what are the positioning mechanisms for these kinds of documents that are out of the document?
1, float

About understanding the document flow in HTML