when using array_walk, the callback function must accept both the value and the key parameters, even if you don't use the key. When using a foreach loop, you can omit the key if it's not needed.
1. Formatting Array Elements
2. Adding a Suffix or Prefix
3. Sanitizing Input Data
4. Collecting Data from Objects
5. Generating HTML Output
6. Applying Conditional Changes
7. Aggregating Data
8. Logging or Debugging