Validation keywords

Validation keywords check the pipeline value. They never replace it. A failed constraint appends an error object to the envelope, and any error empties the final result. Every failed constraint on a pairing reports, so one bad value can carry several errors.

Keyword	Operand	Fails when
type	string number boolean …	the value’s type differs
minimum / maximum	number	the value is below / above
multipleOf	number	the value isn’t a multiple
minLength / maxLength	number	the length is below / above
enum	array	the value isn’t a member
pattern	regex source string	the string doesn’t match
required	true	the value is undefined

A passing constraint is silent:

/age: { source: /age, type: number, minimum: 0 }

{ "age": 41 }

writes 41 with no errors. A failing one reports:

/age: { source: /age, minimum: 21 }

{ "age": 16 }

valid: false
errors:
  - { source: /age, value: 16, minimum: 21, message: cannot be less than 21 }

Error objects carry the read location, the offending value, the constraint with its operand, and a message. See Handle errors.

Constraints check values that exist. On an absent value they are silent, and only required reports the absence:

/v: { source: /missing, minLength: 3 }

with an empty input writes nothing and reports nothing. Each constraint also checks only values of its own type: minLength ignores a number, minimum ignores a string.

Pattern safety

Mapping validation screens pattern values for catastrophic backtracking, using the star-height convention: a quantifier applied to a group that contains another quantifier is an error (KW-pattern-2), and more than 25 quantifiers in one pattern is an error (KW-pattern-3). SPEC §6.7.

mapping:
  /code: { source: /code, pattern: '(a+)+$' }

validates as:

valid: false
errors:
  - rule: KW-pattern-2
    message: pattern must not quantify a group that contains a quantifier
    pointer: /mapping/~1code/pattern
    descriptor: (a+)+$
warnings: []

Evaluation is unchanged; the screen protects consumers that validate before evaluating. It is lexical and conservative: it rejects the dominant catastrophic shapes without proving that accepted patterns match in linear time, and it can reject a pattern that would in fact run fine. Rewrite rejected patterns without nested quantifiers.