Mind maps are indentation-based, unlike the edge families. A central topic sits
at the hub, top-level - (or *) bullets are its branches, and deeper-indented
bullets are their children.
central: (aliases root:, center:) sets the hub, falling back to title:
or the first bare line.
The shallowest bullet indent is the branch level. A deeper bullet nests under
the nearest shallower one, to any depth — a hierarchy is not two levels, and a
repo tree or a taxonomy keeps its shape. Two-space and four-space indentation
both work, and so does a mix.
Six levels below the hub is the ceiling; deeper bullets fold onto their deepest
kept ancestor rather than vanishing.
Branch bullets take [color] and [icon: …]; children take [icon]. A branch's
colour carries down its whole subtree, so depth reads as distance from the hub.