OptionalcontentThe content type.
The relationship id the referencing markup cites this part by.
OptionalnameWhat the part was called where it was read from, so it can be called that again.
OptionalpartsThe parts this one's markup references.
OptionalresourceThe content, for a part that is not markup — an embedded workbook, an image.
The relationship type URI.
OptionalxmlThe markup, for a part that has any.
A document part carried on the model, together with the parts its own markup references.
Remarks
Some of what a spreadsheet contains is not one part but a small tree of them. A chart's markup names a style definition, a color definition, the shapes drawn on top of it, sometimes a whole embedded workbook holding its data; a form control names the part describing what kind of control it is. Each is named by relationship id, so a reference that does not come back makes the document unreadable rather than merely plainer. The whole subtree is carried rather than an enumerated few of it, which is what makes that impossible: nothing referenced can be missing, whether or not this version knows what it was for.
The same shape describes every level,
idandtypebeing the edge from the part that references it.