* YAML allows literal tabs in content, but not indentation.
* Two space indent always preferred.
* Note: YAML dumpers always use 2 space by default.
* '- ...' doesn't need extra indentation.
* Note: YAML dumpers don't use extra indentation.
* There was no mention of single quoted strings. They are preferred
and should be used except when double quote semantics are actually
required. (Best practice).
* Add flow form example for sets: `{a, b, c}`
* Show collapsed form of seq-in-seq: `- - - foo`.
