fn convert_span(
span: &TextSpan,
clusters: &[GlyphCluster],
text_ts: Transform,
) -> Option<(Vec<GlyphCluster>, NonZeroRect)>
fn convert_span(
span: &TextSpan,
clusters: &[GlyphCluster],
text_ts: Transform,
) -> Option<(Vec<GlyphCluster>, NonZeroRect)>