{
  "resourceType" : "Substance",
  // from Resource: id, meta, implicitRules, and language
  // from DomainResource: text, contained, extension, and modifierExtension
  "identifier" : [{ Identifier }], // Unique identifier
  "category" : [{ CodeableConcept }], // What class/type of substance this is
  "code" : { CodeableConcept }, // R!  What substance this is
  "description" : "<string>", // Textual description of the substance, comments
  "instance" : [{ // If this describes a specific package/container of the substance
    "identifier" : { Identifier }, // Identifier of the package/container
    "expiry" : "<dateTime>", // When no longer valid to use
    "quantity" : { Quantity(SimpleQuantity) } // Amount of substance in the package
  }],
  "ingredient" : [{ // Composition information about the substance
    "quantity" : { Ratio }, // Optional amount (concentration)
    "substance" : { Reference(Substance) } // R!  A component of the substance
  }]
}