Started "AtomUnits"

src/mol-model/structure/query/selection.ts

src/mol-model/structure/structure/atom/impl/builder.ts

src/mol-model/structure/structure/atom/impl/properties.ts

src/mol-model/structure/structure/atom/impl/set.ts

src/mol-model/structure/structure/atom/set.ts

src/mol-model/structure/structure/atom/unit.ts

src/mol-model/structure/structure/structure.ts

src/mol-model/structure/structure/symmetry.ts

src/mol-model/structure/structure/unit.ts