function setStop(value, valueState) {
	                stops.push({
	                    value: value,
	                    color: getColorVisual(value, valueState)
	                });
	            }
@example
this.formatValueText(someVal); // format single numeric value to text.
this.formatValueText(someVal, true); // format single category value to text.
this.formatValueText([min, max]); // format numeric min-max to text.
this.formatValueText([this.dataBound[0], max]); // using data lower bound.
this.formatValueText([min, this.dataBound[1]]); // using data upper bound.

@param {number|Array.<number>} value Real value, or this.dataBound[0 or 1].
@param {boolean} [isCategory=false] Only available when value is number.
@param {Array.<string>} edgeSymbols Open-close symbol when value is interval.
@return {string}
@protected