DOM Specification Overview
The genesis of DOM is based on different APIs provided with the browsers such as Microsoft Internet Explorer or Netscape Navigator for accessing HTML documents in the sense that the DOM utilizes the idea of representing documents with an object model, which is accessible to applications through a standard API.
The DOM treats documents as hierarchical tree structures containing objects that represent the components of a document.
Note
A tree is a specially organized collection of objects usually referred to as Nodes. The structure of a tree is organized based on the following rules:
Every node must have one parent node and zero or more child nodes.
The very first node in the tree does not have a parent.
Later in this chapter, we will discuss the organization of XML documents in more detail.
Because most of today's Web documents are HTML based, the DOM API specification has been designed with non-XML tree-structured documents, such as HTML, in mind.
Design Levels
The W3C decided to split the DOM specification into three different levels of implementation, allowing the implementers to choose how much functionality they need to support.
These design levels are
Level 1
Level 2
Level 3