Fossil

      ) || 20,
      chunkFetch: {
        /* Default callack handlers for Diff.fetchArtifactChunk(),
           unless overridden by options passeed to that function. */
        beforesend: function(){},
        aftersend: function(){},
        onerror: function(e){
          console.error("XHR error: ",e);
        }
      }
    }
  };
  /**
     Uses the /jchunk AJAX route to fetch specific lines of a given
     artifact. The argument must be an Object suitable for passing as

    };
    D.clearElement(tr);
    this.e.td = D.addClass(
      /* Holder for our UI controls */
      D.attr(D.td(tr), 'colspan', this.isSplit ? 5 : 4),
      'chunkctrl'
    );
    this.e.msgWidget = D.addClass(D.span(), 'hidden');
    this.e.btnWrapper = D.div();
    D.append(this.e.td, this.e.btnWrapper);
    /**
       Depending on various factors, we need one or more of:

       - A single button to load the initial chunk incrementally

        btnUp = this.createButton(this.FetchType.NextUp);
      }
    }
    //this.e.btnUp = btnUp;
    //this.e.btnDown = btnDown;
    if(btnDown) D.append(this.e.btnWrapper, btnDown);
    if(btnUp) D.append(this.e.btnWrapper, btnUp);
    D.append(this.e.btnWrapper, this.e.msgWidget);
    /* For debugging only... */
    this.e.posState = D.span();
    D.append(this.e.btnWrapper, this.e.posState);
    this.updatePosDebug();
  };

  ChunkLoadControls.prototype = {

                               urlParam/*from fetchChunk()*/,
                               lines/*response lines*/){
      if(!lines.length){
        /* No more data to load */
        this.destroy();
        return this;
      }
      this.msg(false);
      //console.debug("Loaded line range ",
      //urlParam.from,"-",urlParam.to, "fetchType ",fetchType);
      const lineno = [],
            trPrev = this.e.tr.previousElementSibling,
            trNext = this.e.tr.nextElementSibling,
            doAppend = (
              !!trPrev && fetchType>=this.FetchType.FillGap

        }
        Diff.checkTableWidth(true);
        return this;
      }else{
        throw new Error("Unexpected 'fetchType' value.");
      }
    },

    /**
       Sets this widget's message to the given text. If the message
       represents an error, the first argument must be truthy, else it
       must be falsy. Returns this object.
    */
    msg: function(isError,txt){
      if(txt){
        if(isError) D.addClass(this.e.msgWidget, 'error');
        else D.removeClass(this.e.msgWidget, 'error');
        D.append(
          D.removeClass(D.clearElement(this.e.msgWidget), 'hidden'),
          txt);
      }else{
        D.addClass(D.clearElement(this.e.msgWidget), 'hidden');
      }
      return this;
    },

    /**
       Fetches and inserts a line chunk. fetchType is:

       this.FetchType.NextUp = upwards from next chunk (this.pos.next)

       this.FetchType.FillGap = the whole gap between this.pos.prev

       a warning. Returns this object.
    */
    fetchChunk: function(fetchType){
      /* Forewarning, this is a bit confusing: when fetching the
         previous lines, we're doing so on behalf of the *next* diff
         chunk (this.pos.next), and vice versa. */
      if(this.$isFetching){
        return this.msg(true,"Cannot load chunk while a load is pending.");

      }
      if(fetchType===this.FetchType.NextUp && !this.pos.next
        || fetchType===this.FetchType.PrevDown && !this.pos.prev){
        console.error("Attempt to fetch diff lines but don't have any.");
        return this;
      }
      this.msg(false,"Fetching diff chunk...");
      const fOpt = {
        urlParams:{
          name: this.fileHash, from: 0, to: 0
        },
        aftersend: ()=>delete this.$isFetching,
        onload: (list)=>this.injectResponse(fetchType,up,list)
      };

        if( this.pos.prev && this.pos.prev.endLhs >= up.from ){
          up.from = this.pos.prev.endLhs + 1;
          fetchType = this.FetchType.FillGap;
        }
      }
      this.$isFetching = true;
      //console.debug("fetchChunk(",fetchType,")",up);
      fOpt.onerror = (err)=>this.msg(true,err.message);
      Diff.fetchArtifactChunk(fOpt);
      return this;
    }
  };

  /**
     Adds context-loading buttons to one or more tables. The argument