proprietary Google-only format
KML became an international standard of the Open Geospatial Consortium in 2008.
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The KML 2.2 specification was submitted to the Open Geospatial Consortium to assure its status as an open standard for all geobrowsers.
Just FYI, this seems to depend on where you get the Pixel from - if bought directly from Google, it should be offline-unlockable out of the box. The carrier-sold Pixels are a different story because the carriers demanded it.
Of course check this is true for the specific model you’re buying before you actually buy it, but for me the unlock was never greyed out on my 7a.