type:
    Type of value. The followings are available:
     - str
     - int
     - float
     - bool
     - number (int or float)
     - text (str or number)
     - date [NYI]
     - time [NYI]
     - timestamp [NYI]
     - seq
     - map
     - scalar (all but seq and map)
     - any (means any implemented type of data)

required:
    Value is required when true (default is false). This is similar to not-null constraint in RDBMS

enum:
    List of available values.

pattern:
    Specifies regular expression pattern of value. (Uses re.match() )
    pattern rule works in map to validate keys, it is usefull when allowempty is set to True.
    Pattern also works on all scalar types.
    This will be matched against all keys in a map.

regex;<regex pattern>:
    This is only implemented in map where a key inside the mapping keyword can implement this regex; pattern and all keys will be matched against the pattern.
    If a match is found then it will parsed the subrules on that key. A single key can be matched against multiple regex rules and the normal map rules.

range:
    Range of value between max/max-ex and min/min-ex.
    'max' means 'max-inclusive'. (a > b)
    'min' means 'min-inclusive'. (a < b)
    'max-ex' means 'max-exclusive'. (a >= b)
    'min-ex' means 'min-exclusive'. (a <= b)
    Type seq, map, bool and any are not available with range

length:
    Range of length of value between max/max-ex and min/min-ex. Only type str and text are available with length

unique:
    Value is unique for mapping or sequence. This is similar to unique constraint of RDBMS

name:
    Name of schema.

desc:
    Description. This is not used for validation.

allowempty:
    NOTE: Experimental feature!
    Only applies to map. It enables a dict to have items in it that is not validated. It can be combined with mapping to check for some fixed properties but still validate if any random properties exists. See example testfile 18a, 18b, 19a, 19b.

matching-rule:
    NOTE: Experimental feature!
    Only applies to map. This enables more finegrained control over how the matching rule should behave when validation keys inside mappings.
    Currently supported rules is
     - any [This will match any number of hits, 0 to n number of hits will be allowed]