Function slice_content 

pub fn slice_content(
    content: &[TextSpan],
    start: usize,
    end: usize,
) -> Vec<TextSpan>

Slice content by the UTF-16 offset range [start, end). Preserves per-span marks; spans that don’t intersect the range are dropped.

start >= end returns an empty vector. Offsets beyond the content clamp to the end rather than panicking.