Atom Maps:

• The map tells the computer which atoms are which between the reactant and product sides of the reaction.

The map is essentially a 'hint' about the underlying reaction mechanism. The mechanism may or may not be reflected in the connectivity changes over the reaction.

Atom maps are a 'class' property for the atoms in the reaction, excluding the agent atoms.

Values are numbers, without intrinsic meaning. The system may (and does) renumber and reorder them.

Very similar to ring-bond digits: they are interpreted on input, within the toolkit they are 'invisible', the system will generate them on output.

An atom map is optional. Can be omitted, or only partially included.

No requirements for completeness, "chemical sensibility". Independent of the underlying connectivity.