Nesting (supported by some parsers)

[section]
domain = quickref.me
[section.subsection]
foo = bar

The same as JSON below 👇

{
  "section": {
    "domain": "quickref.me"
    "subsection": {
      "foo": "bar"
    }
  }
}

Nest to previous section (shorthand)

[section]
domain = quickref.me
[.subsection]
foo = bar