Practical prototype and part 34: The information in this book is distributed on an "as is" basis, without warranty Although every pre-caution has been taken in the preparation of this work, neither the author(s) nor Apress shall have any liability to any person or entity with respect to any loss or damage caused or alleged to be caused directly or indirectly by the information contained in this work. | PART 2 CHAPTER 9 What You Should Know About DHTML and Dhtml is the term assigned to a collective set of technologies used to create dynamic web content including HTML JavaScript and CSS. The dynamism in DHTML comes from the fact that we re modifying the structure and presentation layers of the document HTML and CSS after the page has been loaded. This definition is broad enough to cover animations elements moving across the page over time new interaction models drag-and-drop and new controls sliders combo boxes and in-place editors . DHTML isn t a special language it s just a term for what becomes possible when the DOM APIs for markup and style are made available to JavaScript. Some of it relies on stable agreed-upon standards like the DOM some of it relies on the mystical APIs that were introduced a decade ago as part of the browser wars. It exists at the intersection of the visual and the analytical making designers and developers equally uncomfortable. We ll deal with the analytical parts as we go. The visual parts require a crash course in CSS concepts and a quick look at the APIs that let us control how elements are displayed through JavaScript. Introducing the CSS Box Model Web design is all about rectangles to put it plainly. Every element represented visually is a rectangle of some sort. That we aren t dealing with circles triangles or irregular polygons is a blessing. Be thankful. Typically these rectangles are placed onto the page in a way that represents their hierarchical relationship. The rectangle created by a table cell for instance will appear inside the one created by its table row. A parent element then acts as a containing block for its children. 193 194 CHAPTER 9 WHAT YOU SHOULD KNOW ABOUT DHTML AND This is the default rendering behavior for most elements because it s a visual conveyance of the elements semantics. Most parent-child relationships have meaning. A list item belongs to an unordered .
