Indicates how the observation-based extraction approach should be applied to an item or all items in a questionnaire. When set to true, the item is extracted as an independent Observation with no relationship to a parent Observation (If true, indicates that the observation-based approach should be used to extract either the particular item (if extension is defined on an individual question or group based on the code present) or all items in the questionnaire (if defined at the questionnaire root and if they have a code present)). When set to a code value (e.g., member or component), the extracted Observation is related to a parent Observation according to the specified relationship. Mixing boolean and code values within the same item is invalid and will result in an error.