The identifier of the custom attribute. Limited to 255 characters in length, cannot begin with a $, and can only contain alphanumeric characters and punctuation.
May be negative to decrement.
Optionalcallback: Callback<boolean>A callback that receives the export function call result.
Increment/decrement the value of a custom attribute. Only numeric custom attributes can be incremented. Attempts to increment a custom attribute that is not numeric be ignored. If you increment a custom attribute that has not previously been set, a custom attribute will be created and assigned the value of incrementValue. To decrement the value of a custom attribute, use a negative incrementValue.