90 		start,  argument
96 		start = start == null ? vp.start : start;
98 		var orgStart = start;
101 			start = Math.min(start, this.visibleNodeList.length - vp.count);
102 			start = Math.max(start, 0, start);
103 			if (start !== orgStart) {
104 				this.debug("Adjust start " + orgStart + " => " + start);
106 					vp.start = start;
110 		return start;
128 						start: this.viewport.start + (ofs > 0 ? 1 : -1),  property
146 			this.viewport.start + this.viewport.count >=
167 			start,
171 			diffVp = { start: 0, count: 0, enabled: null, force: null },  property
177 		this.debug("setViewport(" + opts.start + ", +" + opts.count + ")");
189 		start = opts.start == null ? vp.start : Math.max(0, +opts.start);
191 		start = this._fixStart(start, false);
193 		if (vp.start !== +start) {
195 			newVp.start = start;
196 			diffVp.start = start - vp.start;
235 		vp.start = newVp.start;
373 					if (dy < 0 && viewport.start === 0) {
433 				diff: { start: 0, count: 0, enabled: null, force: null },  property
461 			start = vp.start,
462 			bottom = start + vp.count,
482 		for (i = start; i < bottom; i++) {
622 						start = vp ? vp.start : null;
627 					if (node._rowIdx < vp.start) {
628 						start = node._rowIdx;
629 					} else if (node._rowIdx >= vp.start + vp.count) {
630 						start = node._rowIdx - vp.count + 1;
632 					if (topNode && topNode._rowIdx < start) {
633 						start = topNode._rowIdx;
635 					tree.setViewport({ start: start });  property
646 				start: 0,  property
656 						start: 0,  property
759 				start = viewport && viewport.start > 0 ? +viewport.start : 0,
760 				bottom = viewport ? start + viewport.count - 1 : 0,
782 					(node._rowIdx < start ||
783 						node._rowIdx >= start + viewport.count);
803 					node.tr = tree.tbody.rows[node._rowIdx - start];