Dynamic Navigation with DOM
Taking Advantage of The Document Object Model
By Mark McManus
When the World Wide Web Consortium (W3C) introduced their working draft specification for the Document Object Model (DOM), it detailed how Web browsers should deal with HTML, CSS (Cascading Style Sheets), and XML documents. In particular, the specification describes how all document objects should be accessible programmatically. Ultimately, all Web developers benefit because the DOM provides a clearly defined structure to describe a Web page. Thus, tool developers can map internal object models, which means better tools for Web authors. Web authors get an additional benefit: Knowledge of your document structure makes building dynamic, interactive pages easier.
The initial DOM specification was released after the two major browser vendors (Microsoft and Netscape) released their own implementations, so you can be sure that their versions are somewhat different from the W3C specification. However, because the DOM specification is built from recommendations put forward by a number of companies, neither implementation strays too far from the standard.
This article expands on earlier coverage presented in Web Techniques (see "Introduction to DHTML's Object Model" by Chuck White, December 1997), focusing on element containment and structure navigation. After an overview of W3C recommendations on containment, navigation and modification, I'll present a useful example that implements a collapsible table of contents.
