This property determines the number of columns that will be treated as row headings. When it is set to zero, the grid rows will not have headings. When it is set to a positive value, this value will correspond to the number of columns that will be treated as row headings. For example, if you set the value of this property to 2, the first two records in the grid will be headings. Headings are always visible and can be colored differently from the body of the grid. Specifying more row headers than columns visible in the grid has undefined effects.
This property effectively supersedes the ROW-HEADINGS style. If you specify ROW-HEADINGS, then a NUM-ROW-HEADINGS value of 0 is treated as if it were 1. The ROW-HEADINGS style has no effect when NUM-ROW-HEADINGS is set greater than zero. This rule provides backwards compatibility with ROW-HEADINGS while still allowing for a multi-column row header. (create, modify, inquire)