Otoh, what's the difference between { "number": "1.0000000000000000000000000000001" } along with { "number": { "type": "ModelReal", precision: 64 } }

Otoh, what's the difference between { "number": "1.0000000000000000000000000000001" } along with { "number": { "type": "ModelReal", precision: 64 } } versus <number>1.0000000000000000000000000000001</number> along with <xs:element name="number" type="xs:decimal"/> In each case you have text data given meaning by an external semantics enforced via a schema. The real and unavoidable downside is that JSON actually contains a really lousy primitive. It wouldn't be bad except practically every implementation of JSON automatically performs a lossy coercion to IEEE floats.