Once upon a time, when the web was young and HTML was new, each web page was its own self-contained piece of content. All of the content and formatting that was required for that page was contained on the page itself in the HTML code, and interactive ideas such as JavaScript were mere ideas and not practice. This worked well at first, but then the day came when someone needed to redesign the look of their website. Perhaps colors needed to be changed or a new logo used. Regardless, the whole site had to change, and that meant changing every single page on the site. And no one—literally no one—wants to do that twice.
