LootJS.modifiers((event) => {
    // This covers all vanilla and Biomes O' Plenty grass types in one check
    event.addBlockLootModifier([
        'minecraft:grass', 
        'minecraft:tall_grass', 
        '/biomesoplenty:.*grass/', 
        '/biomesoplenty:.*sprout/',
        '/biomesoplenty:.*bush/'
    ])
    .matchMainHand("#notreepunching:knives")
    .randomChance(0.5) 
    .addLoot("notreepunching:plant_fiber");
});