Block Display

Looking at a normal block. Notice the block icon and name in the top left corner.

By enabling advanced item tooltips, Block Display will also display more advanced information about blocks. Notice the addition of BlockDict entries, resource name and metadata.

When looking at a block that has an inventory, Block Display will show the items inside.

Looking at an entity will reveal its name, icon and health.

By enabling advanced item tooltips, the UUID of the entity will also be revealed.

Mods can add their own custom info to a block using the APIBlockDisplay found in MelonLib. See this Blazeburner for example.