* like MBTiles it's agnostic to what individual tiles are. You can store vector data as SVG, Protobuf, raster PNGs, JPGs or even raw digital elevation models.
* It's not backwards compatible in the same way Cloud Optimized GeoTIFF is.
* It has a recursive index structure to avoid needing to load in huge indexes at once for large datasets (hundreds of millions of tiles).
* It is designed for remote HTTP range reads. If your application can instead directly access a filesytem, like on a mobile phone, MBTiles, which uses SQLite, is a more established solution.
The specification is open source on GitHub https://github.com/protomaps/PMTiles and is still evolving in response to user needs. I've created direct client support for Leaflet and MapLibre, and plan to work on OpenLayers next.