This page that you are reading, for example, lives on a server somewhere in Nevada City, California. Last time I looked it was in a computer sitting on a desk in the corner of a rather large room filled with zillions of racks of modems and computers. There is no monitor on our webserver because all of the files are sent out over the internet not onto a local desk monitor.
So, it's pretty well understood that this page you are reading is constructed from a text file which came to you via modem from Nevada City through a hop-scotch of computer to computer over the internet. Exactly how it gets from computer to computer and makes its way over the internet is a bit of a mystery. But the notion that there is a text file somewhere sitting around for you to request is more or less clear.
But, alas, it's not true. This webpage, as you see it, does not exist anywhere on the internet. It does not exist on any computer in Nevada City or anywhere else. It only exists as potential.
This page is assembled dynamically from separate parts each time that someone requests a look at "http://www.newbie.org/html/lesson15.html". This is a dynamic page. Admittedly we have not made the next leap into storing this page as data in an Oracle database file to be assembled by programs on the fly. We've only broken it into a few parts. The footer is standard, so we keep one copy and use it over and over. That sort of thing.
So, what does this have to do with "Conceptual Walls?"
The ability to work with webpages assembled on the fly from bits and pieces lies on the otherside of a conceptual wall. There are folks that just don't have the ability to wrap their brains around the concept of a webpage being written into bits. For those folks it is much easier to think of webpages as a single text file somewhere. And if those folks were to make the leap into producing their own webpages it would be easier for them to grasp the skills necessary to create a file and move a file. That is a "Conceptual Terrace" upon which they can scramble about comfortably.
So, why am I bring this up?
I am making a plea on behalf of newbies everywhere for software companies, educators, developers, and everyone concerned to allow for "Conceptual Terraces" and "Conceptual Walls".
If you are involved in any way whatsoever in the design of software, please do us all a favor: move the material from a radically higher conceptual terrace into a submenu, or a special popup, or even into a professional interface turned on by altering the options.