The entries of a mapping in the order of the input. The keys are unique. The encoder does not check this for a mapping that a program builds, and a mapping with two equal keys does not read back. Keys are equal as in YAML, e.g. two mappings with the same entries in a different order are equal keys.

A value with a tag that is not the tag of the core schema for it, e.g. !point {x: 1}. A scalar with a tag that the schema does not know is a String inside, e.g. !secret abc.

The encoder writes the tag. Some values read back with a change:

• A value with its own tag of the core schema reads back without Tagged, e.g. Tagged intTag (Int 1) as Int 1.
• A value that does not fit a tag of the core schema does not read back, e.g. a String with intTag.
• A scalar other than a String with a tag that the schema does not know reads back as a String, e.g. Tagged "!x" (Int 5) as Tagged "!x" (String "5").
• YAML has no syntax for the empty tag or a tag of one character, e.g. x or !. The encoder drops such a tag, e.g. Tagged "" (Int 1) reads back as Int 1.
• A node has one tag, so the encoder writes only the outermost tag that it does not drop, e.g. Tagged "!a" (Tagged "!b" (Sequence [])) reads back as Tagged "!a" (Sequence []).

A finite value other than negative zero.

The encoder writes a value whose exponent in scientific notation is beyond the range from -1000 to 1000, e.g. 1.0e+1001, but the decoder rejects it. The decoder never gives such a value, and a Double is always in the range.

Negative zero, e.g. -0.0, which a Scientific cannot hold.