The data cache is a read/write location within an Office Word document or Excel workbook that can be leveraged by your Office application to store needed data. One common scenario is to bind host controls or Windows Forms controls in an actions pane or on a document surface to a data set stored in the document’s data island.
Physically, this data island is implemented as an XML document that is embedded within the Office document. This XML container can host any data type that meets the following two requirements:
It has to be implemented as a read/write public field on the host item (for example, the Word