Yes/No/Don't know, for capturing a common answer set in questionnaires

{
  "resourceType" : "ValueSet",
  "id" : "yesnodontknow",
  "text" : {
    "status" : "generated",
    "div" : "<div xmlns=\"http://www.w3.org/1999/xhtml\">\n      <p>This value set contains 3 concepts</p>\n      <table class=\"codes\">\n        <tr>\n          <td style=\"white-space:nowrap\">\n            <b>Code</b>\n          </td>\n          <td>\n            <b>System</b>\n          </td>\n          <td>\n            <b>Display</b>\n          </td>\n          <td>\n            <b>Definition</b>\n          </td>\n        </tr>\n        <tr>\n          <td style=\"white-space:nowrap\">\n            <a name=\"http---terminology.hl7.org-CodeSystem-v2-0532-Y\"> </a>\u00a0\u00a0\n            <a href=\"http://terminology.hl7.org/5.1.0/CodeSystem-v2-0532.html#v2-0532-Y\">Y</a>\n          </td>\n          <td>http://terminology.hl7.org/CodeSystem/v2-0532</td>\n          <td>Yes</td>\n          <td>\n            <div>\n              <p>Yes</p>\n\n            </div>\n          </td>\n        </tr>\n        <tr>\n          <td style=\"white-space:nowrap\">\n            <a name=\"http---terminology.hl7.org-CodeSystem-v2-0532-N\"> </a>\u00a0\u00a0\n            <a href=\"http://terminology.hl7.org/5.1.0/CodeSystem-v2-0532.html#v2-0532-N\">N</a>\n          </td>\n          <td>http://terminology.hl7.org/CodeSystem/v2-0532</td>\n          <td>No</td>\n          <td>\n            <div>\n              <p>No</p>\n\n            </div>\n          </td>\n        </tr>\n        <tr>\n          <td style=\"white-space:nowrap\">\n            <a name=\"http---terminology.hl7.org-CodeSystem-data-absent-reason-asked-unknown\"> </a>\u00a0\u00a0\n            <a href=\"http://terminology.hl7.org/5.1.0/CodeSystem-data-absent-reason.html#data-absent-reason-asked-unknown\">asked-unknown</a>\n          </td>\n          <td>http://terminology.hl7.org/CodeSystem/data-absent-reason</td>\n          <td>Don't know</td>\n          <td>\n            <div>\n              <p>The source was asked but does not know the value.</p>\n\n            </div>\n          </td>\n        </tr>\n      </table>\n    </div>"
  },
  "url" : "http://hl7.org/fhir/ValueSet/yesnodontknow",
  "identifier" : [{
    "system" : "urn:ietf:rfc:3986",
    "value" : "urn:oid:2.16.840.1.113883.4.642.3.3149"
  }],
  "version" : "5.0.0",
  "name" : "YesNoDontKnow",
  "title" : "Yes/No/Don't Know",
  "status" : "draft",
  "experimental" : true,
  "description" : "For Capturing simple yes-no-don't know answers",
  "compose" : {
    "include" : [{
      "valueSet" : ["http://terminology.hl7.org/ValueSet/v2-0136"]
    },
    {
      "system" : "http://terminology.hl7.org/CodeSystem/data-absent-reason",
      "concept" : [{
        "code" : "asked-unknown",
        "display" : "Don't know"
      }]
    }]
  },
  "expansion" : {
    "identifier" : "urn:uuid:bf99fe50-2c2b-41ad-bd63-bee6919810b4",
    "timestamp" : "2015-07-14T10:00:00Z",
    "contains" : [{
      "system" : "http://terminology.hl7.org/CodeSystem/v2-0532",
      "code" : "Y",
      "display" : "Yes"
    },
    {
      "system" : "http://terminology.hl7.org/CodeSystem/v2-0532",
      "code" : "N",
      "display" : "No"
    },
    {
      "system" : "http://terminology.hl7.org/CodeSystem/data-absent-reason",
      "code" : "asked-unknown",
      "display" : "Don't know"
    }]
  }
}