Writing Parallax Terrain shader

I want to write my Parallax Terrain Shader. I've read in manual that I must write Vertex/Fragment shader because access to Tangent and Bitangent vectors. How to write support for terrain textures like grass, rock, sand and data how to blend them? In what variables there are textures from Terrain Editor, heightmaps, masks etc.? When I add new textures or change existing I must change shader? I'm looking for example shader, any tutorial, manual site or Default Terrain Shader source.