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Provide example of keyword/type applicability. #1

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35 changes: 31 additions & 4 deletions jsonschema-validation.xml
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Expand Up @@ -207,16 +207,43 @@
</t>
</section>

<section title="Keywords and instance primitive types">
<section title="Keyword applicability to instance primitive types">
<t>
Most validation keywords only limit the range of values within a certain primitive type.
When the primitive type of the instance is not of the type targeted by the keyword, the
validation succeeds.
validation succeeds. This is a natural consequence of the "type" keyword validation
operating independently from all other keywords.
</t>
<t>
For example, the "maxLength" keyword will only restrict certain strings (that are too long) from being valid.
If the instance is a number, boolean, null, array, or object, the keyword passes validation.
To illustrate the utility of this behavior, consider that the only way to describe
odd integers is with "multipleOf", which restricts certain numeric values but
successfully validates all other types (string, boolean, null, array, and object).
</t>
<figure>
<preamble>
An odd integer is a JSON number that is a multiple of 1 but not a multiple of 2:
</preamble>
<artwork>
<![CDATA[
{
"type": "number",
"multipleOf": 1,
"not": {
"multipleOf": 2
}
}
]]>
</artwork>
<postamble>
If "multipleOf" automatically imposed a requirement of type number, then that
requirement would be negated by "not". That would mean that an instance would
have to both be a number (to satisfy the outer schema) and not be a number
(to satisfy the negation of the inner schema) in order to successfully validate.
To avoid producing an impossible schema, the instance type must not be constrained
except by the "type" keyword. So in this example, the type is validated by the
outer schema, but left unconstrained within the "not".
</postamble>
</figure>
</section>
</section>

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