HTML

We already know that the final product of the APEX Application Builder is an HTML code, so the importance of this Hyper Text Markup Language (and its successor, the eXtensible version, XHTML) can't be overrated.

The DOM (Document Object Model)

Every element that we are placing on our application page is being translated by the APEX engine, into a combination of HTML, CSS, and in some cases, JavaScript code. As such, all the elements of the page are being arranged in a DOM (Document Object Model) structure a hierarchical, tree-like model. The DOM standard, formalized by W3C (World Wide Web Consortium), allows us to access and manipulate every node on the tree, whether by direct access or by walking up (or down) the tree.

The main building blocks of the DOM are the DOM objects. Every DOM object has a series of properties and methods, and it can include other objects and even a collection of objects (e.g. an array of all images or links on the page).

The two highest objects in the DOM hierarchy...