code: function () {
                  var selectors, s, rules, debugInfo;
  
                  save();
  
                  if (env.dumpLineNumbers) {
                      debugInfo = getDebugInfo(i, input, env);
                  }
  
                  while (true) {
                      s = this.lessSelector();
                      if (!s) {
                          break;
                      }
                      if (selectors) { selectors.push(s); } else { selectors = [ s ]; }
                      this.comments();
                      if (s.condition && selectors.length > 1) {
                          error("Guards are only currently allowed on a single selector.");
                      }
                      if (! $char(',')) { break; }
                      if (s.condition) {
                          error("Guards are only currently allowed on a single selector.");
                      }
                      this.comments();
                  }
  
                  if (selectors && (rules = this.block())) {
                      var ruleset = new(tree.Ruleset)(selectors, rules, env.strictImports);
                      if (env.dumpLineNumbers) {
                          ruleset.debugInfo = debugInfo;
                      }
                      return ruleset;
                  } else {
                      // Backtrack
                      furthest = i;
                      restore();
                  }
              }
docs: div, .class, body > p {...}