src/vs/editor/common/diff/smartLinesDiffComputer.ts/CharSequence/getStartColumn
class CharSequence:	public getStartColumn(i: number): number {
		if (i > 0 && i === this._columns.length) {
			// the start column of the element after the last element
			// is the end column of the last element
			return this.getEndColumn(i - 1);
		}
		this._assertIndex(i, this._columns);
		return this._columns[i];
	}