Choose the loot source method here. 
<p><b>loot</b> Uses a loot table such as <i>minecraft:entities/wither_skeleton</i> or the path to your own custom loot table
<p><b>kill</b> The loot that would be dropped if you killed the specified entity.
<p><b>mine</b> The loot that you would get if the block was mined at the specified co-ordinate. Also determined by the mining tool.
<p><b>fish</b> The loot that you would get if you fished at the specified co-ordinate. Also determined by the fishing rod used.