Given the centrality of the internet today, it is about time for a book like this one. But the web is a dynamic, ever-changing place. The first web browser came into being in 1989 and it did not support colors, images, styling, or scripting. The web today is the result of three decades of evolution driven by market forces, implementation quirks, and the ever-expanding reach of the web. I both hope that this book will remain valuable for years to come, and also hope for dramatic change that makes it obsolete.
This book ignores modern developments like HTTP 2 and Web Assembly. Perhaps a later edition of this book will have to cover them. Nor does this book talk much about hardware virtualization like Web Bluetooth or format centralization like web video. Maybe in the future those will be central to what a browser does.
So in a few years this book could be obsolete, or at least out-dated. But the value of this book goes beyond a point-in-time description of how things work. Many dedicated, brilliant, and talented engineers have devoted themselves to the web over its first three decades. The structure of the web embeds their ideas, inventions, and taste. I hope this book passes them along.