1. 1. Logging
2. 1. 1.1. Getting started with logging in Rust
   2. 1.2. Simple Logger new
   3. 1. 1.2.1. Simple Logger new
      2. 1.2.2. Simple Logger init
      3. 1.2.3. Simple Logger level
   4. 1.3. Logging with log4rs
   5. 1.4. env_logger
   6. 1. 1.4.1. env_logger in a simple way
      2. 1.4.2. env_logger with Builder
      3. 1.4.3. set log level on the command line
3. 2. Tracing
4. 1. 2.1. Tracing demo
   2. 2.2. Tracing in a library
   3. 2.3. Tracing in an application
   4. 2.4. Simple tracing configuration with RUST_LOG environment variable