anchor.diff:      var header = document.querySelector("header");
       var headerHeight = header.offsetHeight;
       
  +    var previousCommands = new Array();
  +    var previousCommandOffset = 0;
  +
       apiCall = function(method, opts, cb) {
           var req = new XMLHttpRequest();
           req.open("POST", "/__better_errors/" + oid + "/" + method, true);
  
positive.code:                             }
                              replPre.scrollTop = replPre.scrollHeight;
                          });
                      }
                  };
              }
          })(i, frames[i], frameInfos[i]);
      }
      
      var applicationFrames = document.getElementById("application_frames");
      var allFrames = document.getElementById("all_frames");
  
negative.code:         if(replInput) {
              replInput.focus();
          }
      }
  
      function populateCommandPrompt(input, newOffset, bound) {
          var index = previousCommands.length + newOffset;
          var previousCommand;
  
          if(index < previousCommands.length && index >= 0) {
              // the new index is within the bounds of the 
              // commands array, so grab the previously
              // entered command.
              previousCommandOffset = newOffset;
              previousCommand = previousCommands[index];
          }else{
              // the new index isn't within the bounds
              // of the array.
              previousCommand = "";
  
              if(index == bound) {
                  // set the offset just outside only
                  // if we're at the bounds of the array.
                  // this is so we only get one 'blank' 
                  // command and don't continue moving
                  // the offset when we shouldn't. 
                  previousCommandOffset = newOffset;
              }
          }
          // now set the input's text to the previous command
          // in the list. 
          input.value = previousCommand; 
      }
      
      for(var i = 0; i < frames.length; i++) {
  