GLSL shader for high quality lighting (glH_MaterialPass=1)?

[raincole]

I'm trying to write my own stylized shaders in Houdini. I've checked https://www.sidefx.com/docs/houdini/shade/opengl.html and https://www.sidefx.com/docs/houdini/shade/glsl.html .

I've also found the code of a default shader in $HFS/houdini/glsl/asset/ogl3_default_glsl_shader.prog, which uses ogl3_default_glsl_shader.frag:
 

if(glH_MaterialPass == 0)
	{
            // Direct lighting pass, compute illumination
	    lamb  = vec3(0.0);
	    ldiff = vec3(0.0);
	    if(has_env_map)
		lspec = vec3(0.0);
	    else
		lspec += vec3(reflect) * mspec * (1-alpha) * 0.5;
	    HOUlightingModel(p, nN, ambient_color,diff,specular_color,
			     metallic_color, lamb, ldiff, lspec,
			     rough, diff_rough, ior, mtl, specular_model,alpha);

#using envLighting
	}
	else
	    lspec = mspec;
    

What does #using envLighting do...? Is #using even a GLSL keyword?