How can I define a specific formula syntax rule for Markdown text?

[1475505]

How can I transfer the formula syntax like ( typora support it）

$$ b = a \times \frac{3}{8} $$

rather than but same process as

$ b = a \times \frac{3}{8} $

？
也就是说，把双美元符号之间的文本 $$——$$ 也解释为数学公式。

[neilmayhew]

This extension is obsolete, and the maintainer has disappeared. Use the forked version instead.