MultiSelect provides SelectionMode property to determine whether you can select one or more than one item from the header. This property lets you choose between the following selection modes through SelectionMode enumeration:

• Single: Allows you to select only one item at a time.
• Multiple: Allows you to select multiple items without holding down a modifier key.
• Extended: Allows you to select multiple consecutive items while holding down the corresponding modifier key.

To set the selection mode to multiple, use the following code:

c1MultiSelect1.SelectionMode = C1.Win.Input.SelectionMode.Multiple;