That is the standard TeX/LateX syntax.
You can check out LaTeX mathematic equation related document about those syntax.
There are some html which explain those [url=]syntax for equations displayed in EJS[/url]. However, it was all written in Chinese (my [url=]Chinese version of physics discussion forum[/url].).

Actually, the equation displayed used in EJS was originally from [url=]HotEqn - Equation Viewer
You can check out their web site for more information.