yq/pkg/yqlib/doc/operators/headers/add.md

Add

Add behaves differently according to the type of the LHS:

• arrays: concatenate
• number scalars: arithmetic addition
• string scalars: concatenate
• maps: shallow merge (use the multiply operator (*) to deeply merge)

Use += as a relative append assign for things like increment. Note that .a += .x is equivalent to running .a = .a + .x.