\Rule - Used to create a MathJax-specific macro giving a rule with a specified width, height, and depth.
{ \Rule <dimenWidth> <dimenHeight> <dimenDepth> }
\Rule command is used to create a MathJax-specific macro giving a rule with a specified width, height, and depth.
x\Rule{3px}{1ex}{2ex}x
x\Rule{3px}{2ex}{1ex}x