# Rustdoc uses CommonMark

for support by default

for support via a flag

Rustdoc lets you write documentation comments in Markdown. At Rust 1.0, we were using the `hoedown` markdown implementation, written in C. Markdown is more of a family of implementations of an idea, and so `hoedown` had its own dialect, like many parsers. The CommonMark project has attempted to define a more strict version of Markdown, and so now, Rustdoc uses it by default.

As of Rust 1.23, we still defaulted to `hoedown`, but you could enable Commonmark via a flag, `--enable-commonmark`. Today, we only support CommonMark.