Tips for inline custom markdown tags?

[ivanjaros]

For block tags, it seems the following pattern is the way to go:

::: foo
...
:::

What about inline tags - what would be a good markdown-friendly pattern? For example, for "spoiler" that would blur text unless users clicks on it, I could imagine !!!...!!! but there are not that many special characters left for more tags. The *_=`~ are already taken. Even ! for image. Is there some guideline on how to come up with inline markdown tags?