BMI with links to Height and Weight

{
  "resourceType": "Observation",
  "id": "bmi-using-related",
  "text": {
    "status": "generated",
    "div": "<div xmlns=\"http://www.w3.org/1999/xhtml\"><p><b>Generated Narrative: Observation</b><a name=\"bmi-using-related\"> </a></p><div style=\"display: inline-block; background-color: #d9e0e7; padding: 6px; margin: 4px; border: 1px solid #8da1b4; border-radius: 5px; line-height: 60%\"><p style=\"margin-bottom: 0px\">Resource Observation &quot;bmi-using-related&quot; </p></div><p><b>status</b>: <span title=\"  ======== need to fix vitals to removed fixed value 'has-member' ==========\n\t&lt;meta&gt;\n\t\t&lt;profile value=&quot;http://hl7.org/fhir/StructureDefinition/vitalsigns&quot;/&gt;\n\t&lt;/meta&gt;\n     \">final</span></p><p><b>category</b>: Vital Signs <span style=\"background: LightGoldenRodYellow; margin: 4px; border: 1px solid khaki\"> (<a href=\"http://terminology.hl7.org/3.1.0/CodeSystem-observation-category.html\">Observation Category Codes</a>#vital-signs)</span></p><p><b>code</b>: BMI <span style=\"background: LightGoldenRodYellow; margin: 4px; border: 1px solid khaki\"> (<a href=\"https://loinc.org/\">LOINC</a>#39156-5 &quot;Body mass index (BMI) [Ratio]&quot;)</span></p><p><b>subject</b>: <a href=\"patient-example.html\">Patient/example</a> &quot;Peter CHALMERS&quot;</p><p><b>effective</b>: 1999-07-02</p><p><b>value</b>: 16.2 kg/m2<span style=\"background: LightGoldenRodYellow\"> (Details: UCUM code kg/m2 = 'kg/m2')</span></p><p><b>derivedFrom</b>: </p><ul><li><a href=\"todo.html\">Observation/bodyheight: Body Height</a></li><li><a href=\"observation-example.html\">Observation/example: Body Weight</a></li></ul></div>"
  },
  "status": "final",
  "category": [
    {
      "coding": [
        {
          "system": "http://terminology.hl7.org/CodeSystem/observation-category",
          "code": "vital-signs",
          "display": "Vital Signs"
        }
      ],
      "text": "Vital Signs"
    }
  ],
  "code": {
    "coding": [
      {
        "system": "http://loinc.org",
        "code": "39156-5",
        "display": "Body mass index (BMI) [Ratio]"
      }
    ],
    "text": "BMI"
  },
  "subject": {
    "reference": "Patient/example"
  },
  "effectiveDateTime": "1999-07-02",
  "valueQuantity": {
    "value": 16.2,
    "unit": "kg/m2",
    "system": "http://unitsofmeasure.org",
    "code": "kg/m2"
  },
  "derivedFrom": [
    {
      "reference": "Observation/bodyheight",
      "display": "Body Height"
    },
    {
      "reference": "Observation/example",
      "display": "Body Weight"
    }
  ]
}