l.TEXTURE_2D, tex, dstMip);

                            // -

                            // ES3.0 p213-214
                            let fbComplete = true;

                            // * "The width and height of `image` are non-zero"
                            fbComplete &= (0 <= dstMip && dstMip <= MIPS-1);

                            if (!tex.immutable) { // "...does not name an immutable-format texture..."
                                // * "...the value of [level] must be in the range `[level