code: function DepthStencilAttachment( fbo, flags ){
    this.fbo   = fbo;
    this.flags = flags;
    this.buffer = null;
    this._depthTexExt = null;
  
    var gl = fbo.gl;
  
    // activate extension and
    // discard depthTex if extension unavailable
    if( this.flags & T_FLAG ){
      this._depthTexExt = gl.getExtension( 'WEBGL_depth_texture' ) ||
                          gl.getExtension( 'WEBKIT_WEBGL_depth_texture' ) ||
                          gl.getExtension( 'MOZ_WEBGL_depth_texture' );
  
      if( this._depthTexExt === null ){
        this.flags = this.flags & ~T_FLAG;
      }
    }
  }
docs: --------------------------------- Depth/Stencil Attachment ---------------------------------