The nice thing about Markdown that doesn't apply to those other formats is that it's designed to read naturally in plaintext. That constraint should (in theory) prevent it from transforming into something prohibitively complicated to write in.
Also, the silly space-at-the-end for line breaks.
I thought it was two spaces at end of line for a line break. Or did the one-space-at-end-of-line argument win?[1]
[1] http://meta.stackexchange.com/questions/40976/what-is-the-re...
And since my editor strips newlines on save (and no, I will not turn that feature off), I guess I can't use it.
Oh well.
It kind of scares me that I might inadvertently strip the newlines out of someone else's markdown that I'm editing, though.
There were some systems back in the DOS/early UNIX era which had significant EOL whitespace. Spaces at the end of a line are still significant following a "\" in shell files. Some early word processors under DOS had significant whitespace at EOL, but tended to display something like a paragraph mark when it mattered.
Python had tab/space trouble at beginnings of lines, but the compiler was finally fixed so that it emits an error if tabs and spaces are mixed in a way which makes indentation visually ambiguous. That was a neat solution to the problem.
Leading tabs in makefiles were a mistake. The author of "make" once wrote that he put that in, and then, the next day, realized it was a bad idea. But he already had a user base of three users and didn't want to change it and break their code.
I thought this idea was dead and buried. Sometimes, they come back.
It would make multiple repeated BRs difficult, though, but you probably shouldn't be doing that anyways.
Intriguing: significant white space on the right-hand side. At least you can see the significant whitespace in Python.
I also have my editor configured to strip trailing whitespace but also to highlight it. People can be very sloppy leaving (insignificant) whitspace lying around in code.
They work like standard Markdown links (text in square brackets, followed by link in parens), except you add a bang in front of it. The bang looks like an upside-down "i", the first letter of "image".
Edit: read too fast; _links_ to images use image instead of text in a link, so you just replace the text with text in square brackets with the syntax of Markdown image. I've never struggled too much with this one, so I don't have any useful mnemonics, sorry.