Writing from fragment shader into 3D render texture

It’s pretty much all in the title, how can I go about rendering into a 3D render texture with a fragment shader?

EDIT: Is there some sort of “layer” input I can use?

Better late than never…

Shader "Custom/Tex3DSlice" {
		_MainTex("3D Texture", 3D) = "white" {}
		_Depth("Depth", Range(0,1)) = 0.5
	SubShader {
			Tags{ "Queue" = "Transparent" "RenderType" = "Transparent" }
			LOD 200
			Cull Off
		// Physically based Standard lighting model, and enable shadows on all light types
		#pragma surface surf Standard fullforwardshadows alpha:fade 

		// Use shader model 3.0 target, to get nicer looking lighting
		#pragma target 3.0

		sampler3D _MainTex;

		struct Input {
			float2 uv_MainTex;

		half _Depth;

		void surf (Input IN, inout SurfaceOutputStandard o) {
			// Albedo comes from a texture tinted by color
			float3 uvw = float3(IN.uv_MainTex.x, IN.uv_MainTex.y, _Depth);
			fixed4 c = tex3D (_MainTex, uvw);
			o.Albedo = c.rgb;
			o.Alpha = c.a;
	FallBack "Standard"