The purpose of this thread is to enable people to check if their formatting works and to play around with their MathJax code.
Quoting from Bill Dubuque's Formatting Sandbox on meta.math.SE:
To use this sandbox, look for a free answer below which says "This answer is free for anyone to use". If one exists then please use it. Else create a new answer. Start writing your answer there. Be sure to save a first draft quickly, to minimize the chance that that someone else concurrently tries to use the same free answer. Then, edit it as often as you like. When you reach a point that you'd like to post it to the intended target answer, simply copy it there and post it.
When your answer is complete and you no longer need the sandbox draft, please "clear" the draft by deleting all of the text and replacing it with the text "This answer is free for anyone to use". This is important because it eliminates TeX code (which may slow down MathJax rendering).