Additionalproperties - sgpinkus/json-schema GitHub Wiki

NOTE: This proposal was incorporated into Draft 04

The validity of an object instance with regards to this keyword depends on its value:

• if it is boolean true or an object, then validation of the instance always succeeds;
• if it is boolean false, then the members (keys) of both properties and patternProperties must be considered, see below.

The value for additionalProperties MUST be a boolean or an object. If it is an object, then this object MUST be a valid JSON Schema.

Boolean value true MAY be considered the same as an empty schema.

This is an example algorithm to determine if the instance is valid:

• construct the following sets:
  • s: the set of members of the instance to validate;
  • p: the set of members of the properties keyword value (if any);
  • pp: the set of members of the patternProperties keyword value (if any);
• remove from s all values in p;
• for each value in pp (which is an ECMA 262 regular expression, see pattern):
  • grab a value of s;
  • try and match it against the regular expression: if it matches, remove it from s;
• the instance is valid if and only if, at this stage, s is empty.

Consider the following schema (note: the regular expression \d matches a single digit):

{
    "properties": {
        "p1": {}
    },
    "patternProperties": {
        "p": {},
        "\\\\d": {}
    }
}

and the following instance to validate:

{
    "p1": true,
    "p2": null,
    "a32&o": "foobar",
    "": "yep, that's a valid member name",
    "finance": "sucks",
    "apple": "victim"
}

The three sets as described by the algorithm above are:

• s: { "p1", "p2", "a32&o", "", "finance", "apple" };
• p: { "p1" };
• pp: { "p", "\\d" }.

After the first step of the algorithm, "p1" is removed from s, which is now:

{ "p2", "a32&o", "", "finance", "apple" }

For the second step:

• "p" matches "p2";
• "\\d" matches "a32&o";
• "p" matches "apple".

Which means s is left with the following values:

{ "", "finance" }

It is therefore nonempty, which means validation fails.