In a flow document, the content adapts itself to fit the container. Flow content is ideal for onscreen viewing. In fact, it avoids many of the pitfalls of HTML.
Ordinary HTML content uses flow layout to fill the browser window. (This is the same way WPF organizes elements if you use a WrapPanel.) Although this approach is very flexible, it only gives a good result for a small range of window sizes. If you maximize a window on a high-resolution monitor (or, even worse, a widescreen display), you'll end up with long lines that are extremely difficult to read. Figure 19-1 shows this problem with a portion of a web page from Wikipedia.
Long lines in flow content
Many websites avoid this problem by using some sort of fixed layout ...