The structure is identical to cultural traits in general, except for a few added fields:

category = string
This is used for grouping in the Add Tradition view, and in the Divergence view.

Layers match the CULTURE_TRADITION_LAYER_PATHS define. Index starts from 0
layers = {
	0 = martial # Use a random icon from the specific subfolder
	# 1 = blah # By leaving out the index, it'll use a random icon from the folder
	3 = letter1.dds # By specifying a file name, that specific file will get used
}

Example:

#dummy_tradition = {
#	parameters = {
#		can_raid = yes
#	}
#
#	character_modifier = {
#		diplomacy = 1
#	}
#
#	county_modifier = {
#		development_growth_factor = 0.05
#	}
#
#	province_modifier = {
#		monthly_income = poor_building_tax_tier_4
#	}
#
#	doctrine_character_modifier = {
#		doctrine = doctrine_pluralism_righteous
#		same_faith_opinion = 5
#		tyranny_gain_mult = -0.25
#	}
#}