What does $$ do in Rstudio markdown document?
<p>I accidentally typed <code>$$</code> somewhere in the markdown portion of my Rstudio markdown document and found that all downstream markdown coding had been turned off. It took me a while to trace the problem to the <code>$$</code>, which appeared in dark-red color.</p>

<p>My question is what does <code>$$</code> do? I have looked in markdown documentations and have not found any references to <code>$$</code>.</p>