title: Understanding the "additionalProperties" keyword in JSON Schema draft version 4
body: <p>Link to the specification: <a href="http://json-schema.org/latest/json-schema-validation.html#anchor64">http://json-schema.org/latest/json-schema-validation.html#anchor64</a></p>
  
  <p>Section 5.4.4.2 states:</p>
  
  <blockquote>
    <p>Successful validation of an object instance against these three keywords depends on the value of "additionalProperties": if its value is boolean true or a schema, validation succeeds; ...</p>
  </blockquote>
  
  <p>Section 5.4.4.3 states:</p>
  
  <blockquote>
    <p>If "additionalProperties" is absent, it may be considered present with an empty schema as a value.</p>
  </blockquote>
  
  <p>Ok, so if "additionalProperties" is absent, it counts as being present with an empty schema. And if it's a schema (of any kind), then the object validates successfully regardless of any other consideration.</p>
  
  <p>But this is contradicted by the assertion in section 5.4.4.5, "Example", that the given instance fails to validate against the given schema (which doesn't specify anything for "additionalProperties").</p>
  
  <p>Can someone explain where and in what way I'm misinterpreting the specification?</p>