This tracking issue comes out of #1525. This feature is still very much up for debate, and this initial post paraphrases the initial definition by @cart from that PR .

Definition

Tags are archetype-specific by-value data that affects archetype identity

Usage

ArchetypeA could have [A, B, C] table components and [D(1)] "tag" component. ArchetypeB could have [A, B, C] table components and a [D(2)] tag component. The archetypes are different, despite both having D tags because the value inside D is different.

Implementation

Tags could potentially build on top of the archetype.unique_components added in #1525 for Resource storage.