Complex sentence: Saint Patrick's Cross (or Saint Patrick's Saltire) is a red saltire (X-shaped cross) on a white field, when considered as a symbol of Ireland or of Saint Patrick, the patron saint of Ireland.
Split into simpler sentences: Saint Patrick's Cross (or Saint Patrick's Saltire) is a red saltire (X-shaped cross) on a white field. The flag is sometimes considered as a symbol of Ireland or of Saint Patrick, the patron saint of Ireland.