File Architecture

Inside the file, the comment content ("Comments1") is expressed separately from the sheet information ("Sheet1"), and separately from the drawing information ("legacyDrawing1") for the containing object:

The parts are related using relationships from the sheet to the comments and drawings parts. Comments are stored together at the sheet-level. Therefore, if there are five worksheets in a workbook, and three of those contain cells with associated comments, there will be three comment parts in the file, one for each sheet.