Boxes and Arrows: Views and Forms: Principles of Task Flow for Web Applications Part 1 – Some pleasantly lucid prose here, viz.:
“[B]ecause the client-server architecture of a web application dictates a serial conversation, these types of operations not only require a broader vocabulary; they also require a separate mode.
Although rich-media applications technologies strive to reduce the division between these modes, when it comes to HTML-based applications, the best strategy is to embrace the nature of the medium.”
Also of interest: ::phpPatterns()