A region of the cell text with its own set of font characteristics.
A cell in a worksheet may contain rich formatted text (RichTextString) grouped into one or more runs. Each run is specified by the RichTextRun object and defines a region of the cell text (RichTextRun.Text) with its own set of font characteristics (RichTextRun.Font). The RichTextString.Runs property provides access to the collection that stores text runs.
To apply rich formatting to the cell text, do one of the following:
Call the CellRange.SetRichText method to assign the rich formatted text to a cell.
For details on how to apply different fonts to specific regions of the cell text, refer to the How to: Apply Rich Formatting to Cell Text document.