:=always has an information field on its left (domicile, risk_level, etc.), and any kind of expression on its right side.
:=to a field, means the field will only be assigned a value based on this condition if it doesn't already have a value. If a user has already provided a value for the field, the system will not override that value.
tax_countrywill be assigned the same value as the field
domicile, unless another value for
tax_countryhas already been provided.
full_namewill receive a value that is the combination of the values in the fields
last_name, separated by a space. Again: only if the field
full_namehasn't already been assigned a value.