The text should be stored using the output format and encoding specified by the parser's ViewerInfoFlags and the outputFormat requested in the dtsMakeViewerParams. The size of the block read is up to the viewer. It must be less than the blockSize supplied in the viewer's dtsViewerInfo, since this is used to allocate the dtsTextBlock's buffer. When all of a file has been parsed, readTextBlock should return an empty text block (no text, zero length). 

If data is returned in a format such as RTF or HTML, the returned data must conform to the specification for that data. For example, if the output format is it_RTF, then the data stored in the dtsTextBlock must be valid RTF.

dtsViewerInfo Structure