Point symbols can themselves consist of other point, line and area subsymbols.
The point symbol editor provides limited support to create point, line and area subsymbols.

In principle, line and area subsymbols can have the same properties as standard line and area symbols. For example, an area subsymbol may have line and pattern fills.
However, the point symbol editor only allows to configure the color of a solid fill and does not support more advanced settings.

Mapper also allows to draw and modify shapes of any color in a much more convenient way than the point symbol editor (see also the feature request in #2383).

Proposal: Extend the point symbol editor to create point, line and area subsymbols from selected objects and add them to an existing point symbol.

Example: Create a North Arrow symbol from area objects

Another example: Merge one point symbol into another by using a point object