A visual media processing method includes performing a conversion between a current video block of a visual media data and a bitstream representation of the current video block, wherein the bitstream representation is configured according to a format rule that specifies that a syntax element is selectively included or excluded in the bitstream representation indicative of a maximum number of merge candidates for a coding tool, thereby indicating whether the coding tool is enabled or disabled for the conversion, wherein the maximum number of merge candidates for the coding tool is zero or a positive number.