code: public Block split(final Line line)
      {
          final Block block = new Block();
  
          block.lines = this.lines;
          block.lineTail = line;
          this.lines = line.next;
          line.next = null;
          if (this.lines == null)
          {
              this.lineTail = null;
          }
          else
          {
              this.lines.previous = null;
          }
  
          if (this.blocks == null)
          {
              this.blocks = this.blockTail = block;
          }
          else
          {
              this.blockTail.next = block;
              this.blockTail = block;
          }
  
          return block;
      }
docs: Splits this block's lines, creating a new child block having 'line' as
  it's lineTail.
  
  @param line
  The line to split from.
  @return The newly created Block.