pub fn prefix_len(&self) -> usize {
        match self {
            CommentVariant::TripleSlash | CommentVariant::DoubleSlashEM => 3,
            CommentVariant::MacroDocEqMacro => 0,
            CommentVariant::MacroDocEqStr(d, p) => d.len() + *p + 1,
            CommentVariant::SlashAsterisk => 2,
            CommentVariant::SlashAsteriskEM | CommentVariant::SlashAsteriskAsterisk => 3,
            _ => self.prefix_string().len(),
        }
    }
Return length (in bytes) of comment prefix for each variant.

By definition matches the length of `prefix_string`.
doc-chunks/src/literal.rs