code: function(parser, reporter) {
          "use strict";
          var rule = this;
  
          var headings = {
              h1: 0,
              h2: 0,
              h3: 0,
              h4: 0,
              h5: 0,
              h6: 0
          };
  
          parser.addListener("startrule", function(event) {
              var selectors = event.selectors,
                  selector,
                  part,
                  pseudo,
                  i, j;
  
              for (i=0; i < selectors.length; i++) {
                  selector = selectors[i];
                  part = selector.parts[selector.parts.length-1];
  
                  if (part.elementName && /(h[1-6])/i.test(part.elementName.toString())) {
  
                      for (j=0; j < part.modifiers.length; j++) {
                          if (part.modifiers[j].type === "pseudo") {
                              pseudo = true;
                              break;
                          }
                      }
  
                      if (!pseudo) {
                          headings[RegExp.$1]++;
                          if (headings[RegExp.$1] > 1) {
                              reporter.report("Heading (" + part.elementName + ") has already been defined.",
                                  part.line, part.col, rule, {0:part.elementName}); // ORION NLS message
                          }
                      }
                  }
              }
          });
  
          parser.addListener("endstylesheet", function() {
              var prop,
                  messages = [];
  
              for (prop in headings) {
                  if (headings.hasOwnProperty(prop)) {
                      if (headings[prop] > 1) {
                          messages.push(headings[prop] + " " + prop + "s");
                      }
                  }
              }
  
              if (messages.length) {
                  reporter.rollupWarn("You have " + messages.join(", ") + " defined in this stylesheet.", rule);
              }
          });
      }
docs: initialization