pub fn add_commonmark(&mut self, origin: ContentOrigin, content: &str) -> Result<()> {
        // extract the full content span and range
        let start = LineColumn { line: 1, column: 0 };
        let end = content
            .lines()
            .enumerate()
            .last()
            .map(|(idx, linecontent)| (idx + 1, linecontent))
            .map(|(linenumber, linecontent)| LineColumn {
                line: linenumber,
                column: linecontent.chars().count().saturating_sub(1),
            })
            .ok_or_else(|| {
                Error::Span(
                    "Common mark / markdown file does not contain a single line".to_string(),
                )
            })?;

        let span = Span { start, end };
        let source_mapping = indexmap::indexmap! {
            0..content.chars().count() => span
        };
        self.add_inner(
            origin,
            vec![CheckableChunk::from_str(
                content,
                source_mapping,
                CommentVariant::CommonMark,
            )],
        );
        Ok(())
    }
Adds a common mark content str to the documentation.
doc-chunks/src/lib.rs