addConditionalFormat method
Adds a conditional-formatting format over the range from start to
end. Multiple rules may target the same or overlapping ranges.
Implementation
void addConditionalFormat(
CellIndex start,
CellIndex end,
ConditionalFormat format,
) {
final sqref = getSpanCellId(
start.columnIndex,
start.rowIndex,
end.columnIndex,
end.rowIndex,
);
_conditionalFormats.add((sqref, format));
}