RE:
https://docs.mongodb.org/manual/core/index-text/#sparse-property
https://docs.mongodb.org/manual/core/2dsphere/#sparse-property
https://docs.mongodb.org/manual/core/2d/#sparse-property

[2d/2dsphere/text] indexes are sparse by default and ignores the sparse: true option.

They also ignore explicitly specifying "sparse:false". The statement should be clarified in these 3 locations to be just "are always sparse and ignore the sparse option".

Somewhat counter-intuitively, specifying "sparse:false" makes the index definition retain it and even print it back on request, clearly showing the "sparse:false" option but it is ignored; SERVER-13808.

These indexes are always sparse no matter what options are passed in.