Groupped Header Column Title

Hello, James,
 
Thank you for contacting us.
 
Our team would like to kindly explain that the cells of the grid can not be united.
 
In case the desired functionality is to add a title to the grid, we recommend using the built-in title property of the grid and chart objects. In their turn, such objects are properties of the options object.
 
Here is an example of how the title can be specified:

options: {
  grid: {
    title: "Title for grid"
  },
  chart: {
    title: "Title for chart"
  }
  ...
}

 
You are welcome to check out an example demonstrating the described approach.
 
More information about the options object and its properties can be found in our documentation.
 
Please let us know if this works fine for you.
Do not hesitate to contact us in case additional questions on this point occur.
 
Best regards,
Illia