If you’re familiar with wireframes, mockups, documentation, etc. for web design then you’ve probably seen grey image placeholders to indicate where an image should go. If you go to Bootstrap’s documentation on thumbnails you’ll see exactly what I’m talking about.
The very first language related to web design I ever learned was HTML. I had a textbook and every online tutorial related to beginning web design starts off with writing simple web pages in pure HTML. After lots of practice I have grown comfortable with writing in HTML and containing everything in tags. So when I started using git (a version control system) and I ran into Markdown I thought “Oh great, some silly little syntax thing I have to learn to use just to write up a README file for git/GitHub/BitBucket…”.