Function write_content_text 

pub fn write_content_text(
    content: &SlideContent,
    options: &TextOptions,
    frames: &mut dyn FnMut(&Shape) -> Option<String>,
    out: &mut String,
)

Appends the text of content to out: shapes in z-order, one shape per line block, paragraphs separated by newlines, table rows one per line with cells separated by the configured separator. Shapes without text contribute nothing. Graphic frames whose text lives in another part (charts, diagrams) ask frames for it. No text is inherited from layouts or masters.