http://hl7.org/fhir/StructureDefinition/observation-precondition|4.0.1

Other preceding or concurrent observations that must be known to correctly interpret the the observation. For example an fiO2 measure taken alongside of a SpO2 measurement. See the [Observation notes](observation.html#notes) section for additional guidance.
element_idtypes
Extension
Extension.extension
Extension.url
Extension.value[x]
Extension
Extension.id
Extension.extension
Extension.url
Extension.value[x]