@Override
    public boolean isExtraField() {
        return isExtraField;
    }
Creates a new field

@param name the name of the field
@param dataType the datatype of the field
@param owner the owning document (used to check for id collisions)
@param fieldMatching the matching object to set for the field
config-model/src/main/java/com/yahoo/schema/document/SDField.java