This example does a few different things at once:

• Players get 33% passive shield damage reduction.
• Players are allowed to use item specific shield overrides.
• Touhou Little Maid maids are allowed to use passive shield DR.
• They use a custom 65% value instead of the normal shared 33%.
• Note: the entity IDs used here are from the 1.12.2 version of Touhou Little Maid. Other versions may use different IDs, for example 1.20.1 uses touhou_little_maid:maid instead of touhou_little_maid:entity.passive.maid. Always check the actual entity ID for your version.
• Non-player entities not in the whitelist do not use passive shield DR by default.
• If applyToAllEntities were enabled, those entities would use their own separate 33% fallback value.
• A specific shield item can use its own custom DR.
• Shield tooltips are enabled.
• The extra item override suffix text is disabled.

general {
    B:enabled=true

    B:applyToPlayers=true
    B:playersUseItemOverrides=true
    D:damageReductionPercent=33.0

    B:applyToAllEntities=false
    D:allEntitiesDamageReductionPercent=33.0

    # Use entityWhitelist if you want an entity to use the normal shared damageReductionPercent value above.
    S:entityWhitelist <
        touhou_little_maid:entity.passive.maid
     >

    # Use entityDamageReductionOverrides if you want an entity to use its own custom value instead.
    # If an entity is listed here, it does not need to also be in entityWhitelist.
    # Overrides take priority over the shared whitelist value.
    S:entityDamageReductionOverrides <
        touhou_little_maid:entity.passive.maid;65.0
     >

    # If true, eligible non-player entities can also use itemDamageReductionOverrides.
    # Entities with their own per-entity override ignore item overrides.
    # Entities using entityWhitelist or applyToAllEntities keep the higher of their normal DR or the item override.
    B:entitiesUseItemOverrides=false

    S:itemDamageReductionOverrides <
        basemetals:diamond_shield;90.0
     >

    B:showShieldTooltips=true
    B:showItemOverrideText=false
}