Cargo Features

[dependencies]
libiio-sys = { version = "0.4.0", default-features = false, features = ["libiio_v0_25", "libiio_v0_21", "libiio_v0_19"] }
default = libiio_v0_25

The libiio_v0_25 feature is set by default whenever libiio-sys is added without default-features = false somewhere in the dependency tree.

libiio_v0_25 default
libiio_v0_24 libiio_v0_23 libiio_v0_21
libiio_v0_19

libiio-sys has 4 features without comments.