String Types

The string type and its email and url shortcuts.

The string type validates text. It has two predefined shortcuts that are string with a built-in pattern: Email and URL.

date, time, and datetime are not string subtypes — they are their own types with their own values. See Date and Time.

For how strings are written (open, quoted, raw), see Strings.

The string family

Type	Is
string	any text
email	string validated against an email pattern
url	string validated against a URL pattern

contact: email, site: url
---
~ [e-mail], 'https://example.com'    # ✓
~ notanemail, 'https://example.com' # ✗ invalid-email

Quote values containing : or spaces (URLs, times-of-day, "Last, First"). An unquoted https://x.com is misread because the open string ends at :.

TypeDef

A string MemberDef accepts only the options below. Any other key is invalid.

Option	Type	Description
type	string	string, email, or url. First positional value.
default	string	Value used when the member is omitted. Second positional value.
choices	array of string	Restricts the value to a fixed set. Third positional value.
pattern	string	A regular expression the value must match.
flags	string	Regex flags for pattern (e.g. i).
len	int ≥ 0	Exact length in characters.
minLen	int ≥ 0	Minimum length.
maxLen	int ≥ 0	Maximum length.
format	string	Serialization form: auto (default), regular, raw.
encloser	string	Quote character used when serializing: " (default) or '.
escapeLines	bool	Whether to escape line breaks on serialization.
optional	bool	If true, the member may be omitted. Shorthand: ? suffix.
null	bool	If true, the member may be null. Shorthand: * suffix.

len precedence. When len is set, minLen and maxLen are ignored.

Constraints

minLen / maxLen / len

name: { string, minLen: 5, maxLen: 20 }
---
~ Ethan              # ✓
~ Alexandra Daddario # ✓
~ Leo                # ✗ invalid-min-length

pattern

A regular expression. Use a raw string (r'…') to avoid escaping backslashes.

ssn: { string, pattern: r'^[0-9]{3}-[0-9]{2}-[0-9]{4}$' }
---
~ '123-45-6789'   # ✓
~ '12345678'      # ✗ invalid-pattern

choices

dept: { string, choices: [cs, mech, civil] }
---
~ cs     # ✓
~ art    # ✗ invalid-choice

Quote choices that look like numbers or contain commas, e.g. ["19.02, 72.85"], so they are treated as strings.

Optional, nullable & defaults

nickname?*: { string, anonymous }   # optional + nullable, default "anonymous"
---
~ {}      # ✓ → "anonymous" (omitted, default applies)
~ N       # ✓ → null
~ John    # ✓ → "John"

Input	Result
valid text	the string
fails a constraint	invalid-* error (invalid-min-length, invalid-pattern, …)
N, nullable (*)	null
N, not nullable	null-not-allowed error
omitted, default set	the default
omitted, optional (?)	absent
omitted, required	value-required error

Use the * suffix for nullability — keyed null: is not yet honored (see below).

Implementation status (beta)

• Keyed optional: works; keyed null: is not yet honored — use the * suffix.

See Also

• Strings (value syntax)

• Email · URL

• Date and Time

• TypeDef · MemberDef