Header grouping is a way to add additional columns above the header grid rows, so that they are grouped in a way you need them.
We support two types of grouping - with colSpan enabled and colSpan disabled.
If the colSpan is disabled (the default) the headers that do not have grouping have a additional cell above it.
If the colSpan is enabled there is no additional cell above the non-grouped column and it is considered as one column.