C1SpellChecker can spell-check controls that derive from Windows.Forms.TextBoxBase. This includes the TextBox and RichTextBox controls.
To spell-check other types of controls (a grid for example), you have to create a wrapper class that implements the ISpellCheckableEditor interface or the ISpellCheckableRichEditor interface.
The ISpellCheckableEditor interface specifies the minimum set of methods and properties necessary to implement modal (dialog-base) spell-checking. The ISpellCheckableRichEditor interface extends ISpellCheckableEditor and specifies additional methods needed to provide as-you-type spell-checking (with the red wavy underlines and spelling suggestions in the context-sensitive menu).
Note: The samples that ship with the C1SpellChecker control include an application called SpellGrid that shows how you can implement the ISpellCheckableEditor interface in a class and use that class to spell-check a C1FlexGrid control.