Cargo Features

[dependencies]
atto = { version = "1.0.10", default-features = false, features = ["onig", "fancy_regex"] }
default = onig

The onig feature is set by default whenever atto is added without default-features = false somewhere in the dependency tree.

onig default

Enables default-onig of syntect

fancy_regex

Enables default-fancy of syntect

syntect:

In order to switch to the fancy-regex engine, disable default features then add the default-fancy feature

Atto has 3 features without comments.