Moves the System.Xml.XPath.XPathNavigator to the first sibling node of the current node.
Returns true if the System.Xml.XPath.XPathNavigator is successful moving to the first sibling node of the current node; false if there is no first sibling, or if the System.Xml.XPath.XPathNavigator is currently positioned on an attribute node. If the System.Xml.XPath.XPathNavigator is already positioned on the first sibling, System.Xml.XPath.XPathNavigator will return true and will not move its position.
If System.Xml.XPath.XPathNavigator.MoveToFirst returns false because there is no first sibling, or if System.Xml.XPath.XPathNavigator is currently positioned on an attribute, the position of the System.Xml.XPath.XPathNavigator is unchanged.