OptionalpartThe chart is carried as the markup it was read from until it is modeled; this is that markup and everything it needs to stay valid — its style and color definitions, the shapes drawn over it, an embedded workbook holding its data. IChart.getXML is the readable view of the chart's own markup; the rest is for writing the chart back out.
OptionalsourceOriginal cNvPr id from the captured source fragment, if any; used to avoid id collisions
with freshly-generated ids on write.
OptionalxmlOpaque source XML fragment, captured verbatim from the source file and replayed as-is on save, for whatever this chart doesn't (yet) model structurally.
The chart's own document part, and the parts that part references.