Implement texture masking into simple existing shader

Questions & Answers
1

Hello,
I have this shader, and I need implement _AlphaTex (black and white texture) as transparent mask for _MainTex.

Shader "Custom/Custom Transparent" {
	Properties {
		_MainTex ("Base (RGB)", 2D) = "white" {}
		_AlphaTex ("Alpha mask", 2D) = "white" {} // I need implement this texture as Transparent mask for _MainText
	}
	SubShader {
	
		LOD 100
	
		Tags
		{
			"Queue" = "Transparent"
			"IgnoreProjector" = "True"
			"RenderType" = "Transparent"
		}
	      
      	Pass
      	{
      		Cull Off
			Lighting Off
			ZWrite Off
			Fog { Mode Off }
			Offset -1, -1
			ColorMask RGB
			AlphaTest Greater .01
			Blend SrcAlpha OneMinusSrcAlpha
			ColorMaterial AmbientAndDiffuse 
      	
         	SetTexture [_MainTex] {Combine Texture * Primary}
      	}
		
	} 
}
2

SetTexture[_MainTex] { combine texture }
SetTexture[_AlphaTex] { combine previous, texture }