4 of 7 Damn you, whomever made me aware of the slanted \TeX output!!!

Can custom TeX/MathJax commands be defined by default for a site?

Recently SE.QuantumComputing started private beta (bit of a misnomer, as users can join freely), and we started a $$\TeX$$-tutorial Meta discussion like the one found here at SE.Math.

Since quantum computing makes frequent use of bra-ket notation and it's a bit tedious to type out the $$\rm\TeX$$ for it constantly, it'd be nice if we could auto-include custom $$\rm\TeX$$ definitions for it, along with other common quantum-computing concepts, in our MathJax implementation.

For example, it'd be cool if we could auto-include

\newcommand{\bra}[1]{\left< #1 \right|}
\newcommand{\ket}[1]{\left| #1 \right>}
\newcommand{\bk}[2]{\left< #1 \middle| #2 \right>}
\newcommand{\bke}[3]{\left< #1 \middle| #2 \middle| #3 \right>}


, so then users could type

• $\bra{x}$ to get $$\left;

• $\ket{y}$ to get $$\left|y\right>$$;

• $\bk{x}{y}$ to get $$\left$$;

etc..

Questions:

1. Does SE.Math or any other SE have such custom-defined $$\rm\TeX$$ commands?
* As [pointed out](https://math.meta.stackexchange.com/questions/28066/can-custom-tex-mathjax-commands-be-defined-by-default-for-a-site#comment114768_28066) by @Quasicoherent in the comments, this has been [proposed before](https://math.meta.stackexchange.com/questions/25283/latex-shortcuts) and rejected.  However, still curious about whether or not it's technically possible in the case that there's broad community agreement on common $$\rm\TeX$$ commands for specialized SE's.

1. If not, is it something that could be reasonably done if the community agrees on a set of highly useful commands?