I prefer to write vectors with the underline symbol:
$\underline{x} \; \underline{x}_k \; \underline{y} \; \underline{z}$
But when I do this in MathJax, the appearence is much different from "normal" LaTeX to PDF workflow; the spacing is much higher.
Normal LaTeX: 
MathJax: 
The underlines in MathJax are placed lower than they should.
How can I adjust the distance between a symbol and its underline in MathJax?
Here an other example:
$\underline{x} \, \underline{\smash{x}} \, \underline{y} \, \underline{\smash{y}}
\quad \underline{x}_k \, \underline{\smash{x}}_k \, \underline{y}_k \, \underline{\smash{y}}_k
\quad \underline{x}{}_k \, \underline{\smash{x}}{}_k \, \underline{y}{}_k \, \underline{\smash{y}}{}_k $
LaTeX:
MathJax:
