You also forgot implicitly concatenated strings.

    "hello" "world"
    blah = (
      "line"
      "line"
    )

They are actually really useful when you want multi-line formatted strings without indentation and had to be made official when people wanted to take them away.

> If you want to be a jerk, you can multiply 4 * 2 * 2 and say "ZOMG 16 string types!!"

And now you understand how they calculated the number of string types in YAML.