Requirements is a concept introduced with Reskillable and is essentially Player-Bound properties to bind items behind.

For example by default, Reskillable has Requirement support for the following:

• Advancements
• Skills
• Traits

This list can be further expanded upon by addons. In-fact CompatSkills adds support for GameStages as a valid Requirement.

The requirement syntax varies from Property to Property on how it's implemented by the addon. Under Requirement Types, you'll be able to see the syntax for all Requirements added by Reskillable and CompatSkills.

See below for a quick list of links to each requirement type.

Links
Links Advancements
Links Dimensions
Links Dynamic Sword Skills
Links GameStages
Links Inverted Requirements
Links Items
Links Logic Operators
Links Ore Dictionary
Links Skills
Links Tool Harvest-Level
Links Traits