So, yes, it's a little complicated ...
However, all implement the basic syntax which is on the daringfireball website. So if that website says that something should happen, it's almost certain to work in any implementation. I say "almost certain" because there are some edge cases where people have made different decisions on which way they should go (for example, we can't write Ti_k_Z correctly here).
]]>In any case, Google takes me to http://daringfireball.net/projects/markdown/syntax, which looks like a canonical reference.
]]>I keep looking for the nice "markdown" syntax page when I'm typing an answer and I can't find it easily in the FAQ, or on the sidebar. I realize it is linked to on the "how to ask" page (which is how I eventually keep finding it), [and now that I'm testing out editing, I realize that the big blue question mark on the formatting bar also goes that page... so I feel pretty silly now] but I think it would be helpful if it were linked to on the sidebar, or perhaps if there was a text label on the formatting bar too.
The sidebar on the page for asking questions does have a helpful list of commands and a link, so perhaps that should be copied onto the answer page so that it is visible when writing an answer.
The flipside of this is that perhaps the interface will be slightly more cluttered, but that seems like a minor price to pay for better-formatted questions and answers.
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