The identifier of the custom attribute. Limited to 255 characters in length, cannot begin with a $, and can only contain alphanumeric characters and punctuation.
The string to be added to the array. Strings are limited to 255 characters in length, cannot begin with a $, and can only contain alphanumeric characters and punctuation.
Optionalcallback: Callback<boolean>A callback that receives the export function call result.
Adds a string to a custom attribute string array, or creates that array if one doesn't exist.