code: private void validateField(FieldDefinition fieldDef) {
          Utils.require(!fieldDef.isXLinkField(), "Xlink fields are not allowed in Spider applications");
          
          // Validate scalar field analyzer.
          if (fieldDef.isScalarField()) {
              String analyzerName = fieldDef.getAnalyzerName();
              if (Utils.isEmpty(analyzerName)) {
                  analyzerName = FieldType.getDefaultAnalyzer(fieldDef.getType());
                  fieldDef.setAnalyzer(analyzerName);
              }
              FieldAnalyzer.verifyAnalyzer(fieldDef);
          }
      }
docs: Validate the given field against SpiderService-specific constraints.