LaTeX macros in markdown
Markdown (in its pure version) only targets HTML and does not know anything about LaTeX. Specifically, if you meant "The markdown supported by tex.stackexchange.com" then the answer is: no, interpreting LaTeX code is not supported. There are many extensions though that support multiple formats as output including LaTeX.
The best tool I know that supports this is Pandoc (see the latex_macros
extension documented here).
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BenSmith
As the world continues to make significant progress in the realm of discrete mathematics and computer science, it remains crucial to investigate their continuous analogies and build dictionaries between these corresponding families of intricate objects. Results of this type provide the freedom to easily transition between equivalent interpretations of mathematical objects for the purpose of viewing them from several angles and hope to extract more valuable information. I work between these realms, building techniques and tools from several areas of modern mathematics that serve to assist in bridging the gaps.
Updated on August 01, 2022Comments

BenSmith over 1 year
I'm wondering if markdown supports even the simplest commands like
\newcommand
\def
\declaremathoperator
Furthermore, whether or not the use of parameters is possible. For example,
\newcommand{\der}[2]{\frac{d #1}{d #2}}

Mico almost 8 yearsWelcome to TeX.SE. Please be a bit more specific as to what you intend to achieve. Is your posting mainly about markdown? If so, it may be offtopic for this site.

BenSmith almost 8 yearsYes I suppose it is. Although I assume any of the TeXsperts who are also active on this page would be familiar with such as task. The point of this question is so that I can paste already written material as answers to mathematical questions here.

egreg almost 8 yearsThis is a Markdown question; note that other sites in the StackExchange network use MathJax, but we don't, because we're mainly interested in seeing the code, rather than an approximate rendering.