The Preview plugin is a visual 'helper' plugin. When clicked, it opens a new window with the contents of the editor
plus any denoted stylesheets and/or styles applied to the page. This is useful for when you are editing content
that will be displayed with styles different from what the editor applies. When you click preview, a new window will open
with the styled content. The styles chosen are not necessarily pretty, just something to make it very obvious styles are being applied.