The Markdown Editing Help page on Chemistry Stack Exchange (https://chemistry.stackexchange.com/editing-help#latex) includes the following short example for the the use of MathJax:
$$
\Gamma(z) = \int_0^\infty t^{z-1}e^{-t}dt\,.
$$
This example would render as follows:
$$ \Gamma(z) = \int_0^\infty t^{z-1}e^{-t}dt\,. $$
This example is not strictly wrong; however, it contains a few small typographic nonconformities (the positions of the limits of the definite integral; the mathematical constant $\mathrm e$ as well as the $\mathrm d$ in the derivative $\mathrm dt$ shall not be set in italics; there shall be a thin space before the $\mathrm d$, which is not automatically set by MathJax; and the wrong space before the final punctuation mark, which makes the result look like bad kerning).
The correct expression should look like this:
$$ \Gamma(z) = \int\limits_0^\infty t^{z-1}\mathrm e^{-t}\,\mathrm dt. $$
On Chemistry Stack Exchange (in contrast to the communities of some other Stack Exchange sites or the terrible user interface of Stack Exchange itself), we try to encourage our users to use typesetting in accordance with international standards for science and technology.
Therefore, the example included in the Markdown Editing Help page should be changed so that it yields a correct result, for example:
$$
\Gamma(z) = \int\limits_0^\infty t^{z-1}\mathrm e^{-t}\,\mathrm dt.
$$
\rm
alive, actually only giving us a thin line to some other hellish formatting... $\endgroup$