fn trim_span(content: &str, span: &mut Span, pre: usize, post: usize) {
    span.start.column += pre;
    if span.end.column >= post {
        span.end.column -= post;
    } else {
        // look for the last character in the previous line
        let previous_line_length = content
            .chars()
            .rev()
            // assumes \n, we want to skip the first one from the back
            .skip(post + 1)
            .take_while(|c| *c != '\n')
            .count();
        span.end = LineColumn {
            line: span.end.line - 1,
            column: previous_line_length,
        };
    }
}
Adjust the provided span by a number of `pre` and `post` characters.
doc-chunks/src/literal.rs