DEVELOPER GUIDE

General Guidelines

When you create an event or decision, always leave a comment so other developers can know context.
Try to use weight_multiplier instead of mean_time_to_happen, it makes the mod less CPU intensive.
Add pre-triggers as much as possible, this also makes the mod less CPU intensive.
There's custom Notepad++ language Guardians of Azeroth\coder_resources\CK2 Language.xml. It's very desirable to instal it. This will highlight the syntax of CK2 and will allow to use Right Click > Toggle Single Line Comment, Block Comment and Block Unmomment functions to comment out multiple lines.

To instal:

Open Notepad++ and open the "Define Your Language" tool in the "Language" menu
Click "Import" and select the Guardians of Azeroth\coder_resources\CK2 Language.xml file.
Make sure to hit "Save As" in the Define Your Language tool. Type anything you want as the name, it isn't important.
Select the new language in the "Language" menu.

There must be a gap (line without any text) between the numbered groups written below. In essence, all conditions in the same number group will occur together in one code block. For example, a space will exist between has_dlc and ai.

has_dlc, is_untouchable_trigger, can_rule_peacefully_trigger
ai, is_playable, is_adult, is_incapable, prisoner, is_inaccessible_trigger
is_ruler, is_landed, independent, same_realm, mercenary, holy_order, is_tributary, government, tier, war
character, is_within_diplo_range, cooldowns, limit of attempts or flags/traits/modifiers that are set if an event/decision is ongoing or happened.
Being type (being_ trait) , race (creature_ trait), class (class_ trait), mana triggers (has_5_mana_trigger, has_4_mana_trigger etc) religion, culture, +other traits
Wealth, piety, prestige, and user variables
Other conditions

show_scope_change, save_event_target_as
Cooldowns, limit of attempts or flags that are set if the event/decision is ongoing
Being type (being_ trait) , race (creature_ trait), class (class_ trait), mana effects (add_5_mana_effect, remove_5_mana_effect, clear_mana_modifier_effect etc) religion, culture, +other traits
Wealth, piety, prestige, and user variables
Other effects
Continuation of an event chain
Death

Utilize the order given in this article making a gap between the modifiers similar to how they are sectioned off. For example "Character Attribute Modifiers" and "Realm Modifiers".