code: function validateSrc (src, isImageCb, isVideoCb) {
    checkIsImage(src, function isAnImageUrl (isImage) {
      if (isImage) {
        isImageCb(src);
        return;
      }
      isVideoCb(src);
    });
  }
docs: Validate a texture, either as a selector or as a URL.
  Detects whether `src` is pointing to an image or video and invokes the appropriate
  callback.
  
  `src` will be passed into the callback
  
  @params {string|Element} src - URL or media element.
  @params {function} isImageCb - callback if texture is an image.
  @params {function} isVideoCb - callback if texture is a video.