RGB 0..=1 background, or null for no shading.
OptionalbordersPer-cell borders [top, right, bottom, left] (same shape as the
paragraph borders). Omitted = no per-cell regime: the table-wide
GigaTable.border applies. When present, a null side draws nothing
(an explicit "no line here"). Present since 0.117.0.
A table cell: block content, span, and optional RGB shading (
model::Cell).