The grid area model in which overlaps RowIndicator and HeaderSummary.
It is created when initializing HeaderSummary, and is used as HeaderSummary.head property. You do not need to directly create this class object.
grid.setOptions({
header: {
summary: {
head: {
text: "\u03a3", // sigma
styles: {
fontItalic: true,
color: '#800'
}
}
}
}
});