value() {
        return new ArgHandler("_RichText.value")
            .case(() => {
                return this._valueNode.children[0];
            })
            .case('string', value => {
                value = value.replace(/(?:\r\n|\r|\n)/g, '\r\n');
                const hasLineSeparator = value.indexOf('\r\n') !== -1;
                this._valueNode.children[0] = value;
                if (value.charAt(0) === ' ') xmlq.setAttributes(this._valueNode, { 'xml:space': 'preserve' });

                if (this._richText) this._richText.removeUnsupportedNodes();
                if (hasLineSeparator) {
                    // set wrapText = true if it contains line separator, excel will only display new lines if it sets.
                    if (this._richText.cell) {
                        this._richText.cell.style('wrapText', true);
                    }
                    xmlq.setAttributes(this._valueNode, { 'xml:space': 'preserve' });
                }
                return this;
            })
            .handle(arguments);
    }
Sets the value of this part of rich text
@param {string} text - the text to set
@return {RichTextFragment} - RichTextFragment