Minecraft wiki entry for Development_versions, associated text: Added a new number display to track progress while completing certain advancements
Added the changed_dimension trigger
Takes two optional conditions: to and from, both being strings that accept "overworld", "the_nether", or "the_end".
Without the conditions, you can check if the player travels to any dimension from any dimension.
The "location" shared object has a new dimension string (same values as above).