Why 0 is used in &mt_home, &mt_end, and &smart_num?

[numToStr]

I was looking at the keymap and saw that 0 is being used in &smart_num hold-tap modifier. But i couldn't understand why, does it mean something or is it just a placeholder due to bindings syntax?

zmk-config/config/base.keymap

Line 112 in de65ae6

#define SMART_NUM &smart_num NUM 0

zmk-config/config/base.keymap

Lines 84 to 85 in de65ae6

	#define NAV_LEFT &mt_home 0 LEFT // tap: left | long-tap: beginning of line
	#define NAV_RIGHT &mt_end 0 RIGHT // tap: right | long-tap: end of line

[urob]

TL;DR; It's a dummy parameter since we are only needing one parameter but the hold-tap expects two. The official docs go into a bit more details: https://zmk.dev/docs/behaviors/hold-tap#using-different-behavior-types-with-hold-taps