Consider replace `[in]` with `**in**` or something similar.

[Jisu-Woniu]

Rustdoc uses Markdown syntax, and in Markdown, a bracket denotes a link or <a> element in page.

So a [in] (or [out], etc.) in output Rustdoc may be rendered as "in" in VS Code or maybe other editors. So it needs to be replaced or escaped.

What's worse, in my customer's C++ codebase, they wrote [in][out] instead of [in, out], so the output Rustdoc became in, the [out] was completely hidden.

I have some suggestions:

• Escape all [in] as \[in\] so it renders correctly as [in], or
• Replace [in] with *in* or **in** so it gets rendered as italic or bold form
• Use other syntaxes which does not have other meanings in Markdown / Rustdoc