A video processing method is provided to comprise: performing a conversion between a current video block of a video and a coded representation of the current video block, wherein the coded representation conforms to a format rule specifying that a syntax element corresponding to side information of a secondary transform tool for the current video block is signaled in the coded representation before transform related information, wherein the secondary transform tool includes applying, during encoding, a forward secondary transform to an output of a forward primary transform applied to a residual of a video block prior to quantization, or applying, during decoding, an inverse secondary transform to an output of dequantization of the video block before applying an inverse primary transform.