fhirpath.js

When evaluating weight(), the engine searches for the first available score extension for each source node using the following priority order:

1. Source Node: Check the source node itself for a score extension.
2. QuestionnaireResponse Answers: If the source node is an answer from a QuestionnaireResponse or its value[x]:
   • Check the value[x] element for a score extension.
   • Check the corresponding answer option (if any) of the corresponding Questionnaire item for a score extension.
   • If the Questionnaire item references a contained ValueSet, check the corresponding element there for a score extension.
3. Local CodeSystem: If the source resource (e.g., QuestionnaireResponse) or Questionnaire contains a corresponding CodeSystem, check for a score extension (R4) or property (R5) there.
4. Terminology Server: Look for a score extension (R4) or property (R5) in the corresponding CodeSystem loaded from a remote terminology server.

htmlChecks() enforces two main categories of rules: FHIR narrative rules and XML well-formedness.

FHIR Narrative Rules

• Allowed Elements/Attributes: Only elements and attributes permitted by the FHIR narrative rules (based on HTML 4.0 chapters 7-11 and 15) are allowed.
• Images: <img> is allowed, but image maps (<map>, <area>) and their attributes (usemap, ismap) are rejected.
• Anchors: <a> elements may carry name or href (or both). Other anchor attributes like charset, type, hreflang, rel, and rev are rejected.
• Tables: width is accepted on <table> and <img> only. Other table attributes like abbr, align, axis, char, charoff, colspan, headers, rowspan, scope, span, and valign are accepted on any element.
• Prohibited Content: Scripts, forms, objects, frames, iframes, head, body, base, link, xlink:*, deprecated elements, and event-related attributes (e.g., onClick) are rejected.
• Content Requirement: The div must have non-whitespace content (text or an <img> with a src attribute).
• Entities: HTML entities like   are not supported. Use Unicode characters or numeric character references (e.g.,  ) instead.
• Namespaces: A default namespace declaration is optional but must be the XHTML namespace (http://www.w3.org/1999/xhtml).

XML Well-formedness

• Closing Tags: Every element must be closed (<br></br>) or self-closed (<br/>). HTML void-element shorthand (e.g., <br>) is rejected.
• Attributes: Must have quoted values (<p class="c">) and be separated by whitespace.
• Characters: Raw < is not allowed in attribute values. Only legal XML characters are permitted (no C0 control characters except tab, LF, and CR).
• Comments: Must not contain -- and cannot end with -.
• Prohibited XML structures: <!DOCTYPE> declarations and <![CDATA[ sections are not allowed.
• Namespaces: Namespace prefixes are not supported. Only a default xmlns declaration is accepted.

When using third-party authentication (such as OAuth2) to access FHIR servers or terminology servers, you can provide authentication credentials via the httpHeaders option in the fhirpath.evaluate options object.

To use this, map the server's base URL to an object containing the required headers. If you are using the fhirclient npm package, you can pass the header obtained from client.getAuthorizationHeader() directly into this configuration.

FHIR.oauth2.ready().then(client => {
  const res = fhirpath.evaluate(
    {"resourceType": "QuestionnaireResponse", ...},
    '%context.repeat(item).answer.weight().sum()',
    {},
    fhirpath_r4_model,
    {
      async: true,
      terminologyUrl: 'https://some-server',
      httpHeaders: {
        'https://some-server': {
          // Use the same Authorization header as fhirClient
          Authorization: client.getAuthorizationHeader()
        }
      }
    }
  );
});