Function convert_for_dollar 

pub fn convert_for_dollar<'a>(
    source: &'a str,
    range: &Range<usize>,
    span: &MathSpan,
) -> Cow<'a, str>

Rewrite the source bytes of a math region to dollar delimiters.

range is the outer byte range (delimiters + body, in source). span is the scanner-tagged classification.

• MathSpan::Environment: borrow source unchanged — there is no dollar form of \begin{name}…\end{name}.
• MathSpan::Inline: emit ${body}$.
• MathSpan::Display: emit $$ {body} $$.

The body is read through super::span::MathBody::as_str, which already strips container prefixes (blockquote >, list-item continuation indentation). Hand-slicing the source and stripping the delimiters here would re-do that work and silently break for container-nested math.