The concept behind the illuminated manuscript is very simple—it is a (usually medieval) book, with beautiful, intricate, ornate illustrations. They usually contained content of a religious or stately nature, although I will only be advocating for their style to live on, and not their content.
They embody the idea of simple complexity, making them perfect for use with a computer.
Simple Complexity
Simple complexity is something we see all throughout the ancient and medieval world. By simple complexity, I mean the stretching of a simple idea as far as it will go. An example of this is the pipe organ, which at its heart uses only the principle of blowing air through different-sized tubes. The medieval people took this idea, and created grand organs, with hundreds of pipes, each controlled by tiny wooden rods. This, however, did not require any substantial new science, thinking, or improvement of the concept itself—just painstaking detail and patience.
The same is true with the illustrations in an illuminated manuscript. Being created before the Renaissance, medieval authors did not know of perspective, anatomy, or any of the other knowledge needed to make art. They took simple patterns, geometric shapes, and flat drawings, and repeated and ornamented them with such a level of detail as to make them beautiful.
How it fits with the computer
What this means is that *you* can make illustrations just as beautiful, with no learning or training. Because they require neither knowledge nor skill to produce. Just painstaking detail. Of course, you likely do not have the countless hours that medieval illustrators had to produce their masterpieces. However, you have a computer, capable of repeating, endless, beautiful patterns, with a mere ctrl+c, ctrl+v. This is, of course, in addition to it being easier to paint pixels yellow than to go through the arduous process of gilding a page (an interesting old-web site for how they did this can be found here).HTML gives you all the tools you need to create your own illuminated manuscript for the modern era. Beautiful borders and backgrounds (or ugly ones like you can see on my site), large images placed wherever you like, and even something beyond the manuscript with animated gifs, can be yours with HTML. Of course, you have other options, too. A well-crafted PDF can give you an illuminated manuscript with a beautiful interplay between text and images, guaranteed to look the same regardless of the device it's being viewed from.
They are a highly powerful medium
There is a reason why the illuminated manuscript was used by the Church, and by the State. It is because it is a highly powerful way of getting information across. The decorations on this page are not particularly powerful and are thus not a good example. Firstly, this page uses my default web style, so the illuminations (if you can even call them that) are not particularly relevant to the content. Secondly, this is just a small opinion piece, so of course, it will not be as powerful as the typical content that fills an illuminated manuscript.
However, the right content, combined with the right illuminations, can produce something incredibly powerful. Combining artwork with literature creates something uniquely elevated. A brilliant example of this is the legendary Saint John's Bible, pictured below. Carl Jung's Liber Novus also contains many brilliant illuminations, and it shows what the devoted amateur can do.
If you have a horror story, or a manifesto, or a treatise on love, death, war, or power, or some other serious nonsense, then I reccomend you consider turning your text to an illuminated manuscript, be it one of html, or of pdf, or of something else, to give it that extra spookiness, beauty, power, and importance. You can also create illuminated poetry.
PS --- Not all illuminated manuscripts are created equal, and to say that they don't require knowledge of art or talent would be reductive. Many of them require massive skill to create, even with the aid of a computer. Many of them use perspective or render beautiful human faces. But yours don't have to if you don't have the skill for it.