required, additionalProperties, propertyNames, dependentRequired and any other validators that reference property *names* need a way to indicate the erroring names in ValidationErrors

Trying to figure out if there is a way to retrieve the name of a missing required property from an error (without hacking it out of error.message).

For example:

from jsonschema import Draft4Validator as Validator

schema = {
    'type': 'object',
    'properties': {
        'a': {
            'type': 'string'
        },
        'b': {
            'type': 'string',
            'pattern': '^hello$'
        }
    },
    'required': ['a', 'b']
}

errors = Validator(schema).iter_errors({'b': 'world'})
for error in errors:
    print error.path, error.schema_path, error.message

# deque([]) deque(['required']) 'a' is a required property
# deque(['b']) deque(['properties', 'b', 'pattern']) 'world' does not match '^hello$'

In error.path and error.schema_path there is no mention of 'a'. Is there a way to determine that the property missing was 'a' without using error.message?

Start by reviewing ValidationError's existing path, schema_path, and message fields, then inspect how the required, additionalProperties, propertyNames, and dependentRequired validators construct errors. Done means the relevant errors expose offending property names directly, with tests covering missing and invalid property-name cases without parsing error.message.