The chart's own document part, and the parts that part references.
Remarks
The parts the chart needs to be written back: its style and color definitions, the shapes
drawn over it, an embedded workbook holding its data. The part's own markup is kept only while
the chart still states what it was read from, so an untouched chart is written back as it was.
OptionalsourceId
sourceId?:number
The id the chart's frame had in the file it was read from. A writer keeps it where it is
free in the drawing, so references to the frame by id still find it.
The chart: every chart type, its data, axes, text and formatting.