Understanding Device tree Syntax

i am looking at a dts file which tries to specify different nodes but interestingly i find few nodes having different style of nomenclature

/ {
    model = "TI AM335x BeagleBone Black";
    compatible = "ti,am335x-bone-black", "ti,am335x-bone", "ti,am33xx";
};

&ldo3_reg {
    regulator-min-microvolt = <1800000>;
    regulator-max-microvolt = <1800000>;
    regulator-always-on;
};

&mmc1 {
    vmmc-supply = <&vmmcsd_fixed>;
};

&mmc2 {
    vmmc-supply = <&vmmcsd_fixed>;
    pinctrl-names = "default";
    pinctrl-0 = <&emmc_pins>;
    bus-width = <8>;
    status = "okay";
};

/ { hdmi { compatible = "ti,tilcdc,slave"; i2c = <&i2c0>; pinctrl-names = "default", "off"; pinctrl-0 = <&nxp_hdmi_bonelt_pins>; pinctrl-1 = <&nxp_hdmi_bonelt_off_pins>; status = "okay"; }; };

what does it convey if a node has & as its prefix more over what is the necessity of separating them from root node, while they can be present in the root node itself ? interestingly the above example also has two root nodes how is that possible