xml-naming

Validates XML name productions as defined in the XML 1.0 and XML 1.1 specifications.

Covers all five productions:

Production	Description	Colon	Digit/hyphen start
Name	General XML name	✅	❌
NCName	Non-Colonized name	❌	❌
QName	Namespace-qualified name (prefix:local)	✅ (one only)	❌
NMToken	Name token (relaxed start)	✅	✅
NMTokens	Whitespace-separated NMToken list	✅	✅

Used internally by fast-xml-parser, fast-xml-validator, @nodable\flexible-xml-parser and fast-svg-parser.

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Install

npm install xml-naming

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Usage

Boolean validators

import { name, ncName, qName, nmToken, nmTokens } from 'xml-naming';

// Name — colon allowed anywhere, used for DOCTYPE entity names
name('foo')          // true
name('a:b:c')        // true  ← multiple colons fine for Name
name('1foo')         // false ← digit start invalid

// NCName — no colon, used for SVG id attributes, namespace prefixes
ncName('my-id')      // true
ncName('xlink:href') // false ← colon not allowed

// QName — exactly one colon as prefix separator, used for element/attribute names
qName('svg:circle')  // true
qName('foo')         // true  ← unprefixed QName is valid
qName('a:b:c')       // false ← only one colon allowed
qName(':foo')        // false ← cannot start with colon

// NMToken — any NameChar at start, used for DTD NMTOKEN attributes
nmToken('123')       // true  ← digit start is fine
nmToken('-bar')      // true
nmToken('foo bar')   // false ← space not allowed

// NMTokens — whitespace-separated NMToken list
nmTokens('tok1 tok2 -foo 123')  // true

XML version option

All validators accept an optional { xmlVersion } option:

import { name } from 'xml-naming';

name('\u0085', { xmlVersion: '1.0' })  // false — NEL (Next Line), not in 1.0 ranges
name('\u0085', { xmlVersion: '1.1' })  // true  — explicitly allowed in 1.1

name('\uD800\uDC00', { xmlVersion: '1.0' })  // false
name('\uD800\uDC00', { xmlVersion: '1.1' })  // true

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ASCII-only fast path

All validators, validate, validateAll, and sanitize also accept { asciiOnly: true }. When set, matching is restricted to the ASCII subset of the NameStartChar/NameChar productions and skips unicode-aware regex matching entirely — no \u00C0-\uFFFD-style ranges, and (for XML 1.1) no /u regex flag. Unicode-aware regexes are measurably slower than plain ASCII matching in JS engines, so this is a real performance win when you know your input is ASCII-only, which is the common case for HTML/SVG ids and most XML tags.

This is opt-in and defaults to false for backward compatibility: turning it on changes behavior, since it rejects legitimate non-ASCII XML names that would otherwise be valid. Only enable it when you control the input and know it's ASCII (e.g. internal identifiers, machine-generated names), not for validating arbitrary user- or externally-supplied XML/SVG content.

import { name, sanitize } from 'xml-naming';

name('café', { asciiOnly: true })   // false — 'é' is not ASCII, even though it's
name('café')                        //  true    a valid XML 1.0/1.1 NameChar

sanitize('café', 'name', { asciiOnly: true })  // 'caf_' — non-ASCII replaced too
sanitize('café', 'name')                       // 'café' — left untouched by default

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Memoized validator (createValidator)

Real documents tend to reuse a small vocabulary of tag/attribute names across many siblings (id, class, href, ... repeated across hundreds of elements). Calling the plain boolean validators re-runs the regex on every call, even for names seen before.

createValidator(production, opts) returns a memoized validator function: xmlVersion and asciiOnly are fixed at creation time (so the regex is resolved once, not per call), and repeated inputs after the first are served from an internal cache instead of re-matching the regex.

import { createValidator } from 'xml-naming';

const isQName = createValidator('qName', { xmlVersion: '1.0' });

isQName('sku');   // false → regex test (cache miss), result cached
isQName('sku');   // false → cache hit, no regex run

Use one instance per document/parse (or reuse across a session — your choice), rather than creating one per call:

// e.g. inside a parser, once per parse call:
const isValidTag = createValidator('qName', { asciiOnly: true });

for (const tagName of tagNames) {
  if (!isValidTag(tagName)) throw new Error(`Invalid tag name: ${tagName}`);
}

Because the validator is a plain function, this loop already gets short-circuit behaviour (via break/throw on first failure) and zero extra allocation on the happy path — no separate "bulk" API is needed for that.

Cache bound: the internal cache is capped by maxCacheSize (default 2048). Once the cap is reached, new distinct strings are still validated correctly, they're just no longer cached — existing cached entries keep being served. This keeps memory bounded even against high-cardinality or adversarial input (e.g. externally-supplied names that never repeat), without the cost of a full LRU or the perf cliff of reset-and-refill.

Call .reset() on the returned function to clear the cache manually, e.g. between unrelated parse calls if you're reusing one validator instance across a long-running process:

isQName.reset();

The cache is private to each createValidator() instance — there's no shared/global cache, so unrelated callers never interfere with each other.

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Diagnostic validation

import { validate } from 'xml-naming';

validate('svg:circle', 'qName')
// { valid: true, production: 'qName', input: 'svg:circle' }

validate('1foo', 'ncName')
// {
//   valid: false,
//   production: 'ncName',
//   input: '1foo',
//   reason: 'First character "1" is not a valid NameStartChar',
//   position: 0
// }

validate('foo:bar', 'ncName')
// {
//   valid: false,
//   production: 'ncName',
//   input: 'foo:bar',
//   reason: 'Colon is not allowed in NCName',
//   position: 3
// }

validate('a:b:c', 'qName')
// {
//   valid: false,
//   production: 'qName',
//   input: 'a:b:c',
//   reason: 'QName can have at most one colon',
//   position: 3
// }

---

Batch validation

import { validateAll } from 'xml-naming';

validateAll(['svg', 'circle', '123bad', 'xlink:href'], 'ncName')
// [
//   { valid: true,  production: 'ncName', input: 'svg' },
//   { valid: true,  production: 'ncName', input: 'circle' },
//   { valid: false, production: 'ncName', input: '123bad',    reason: '...', position: 0 },
//   { valid: false, production: 'ncName', input: 'xlink:href',reason: '...', position: 5 }
// ]

---

Sanitize / auto-fix

Useful when generating XML/SVG programmatically from user-supplied strings:

import { sanitize } from 'xml-naming';

sanitize('123abc',    'ncName')  // '_123abc'   ← digit start fixed
sanitize('my element','name')   // 'my_element' ← space replaced
sanitize('foo:bar',   'ncName') // 'foobar'     ← colon stripped
sanitize('hello!',    'name')   // 'hello_'     ← illegal char replaced

// Custom replacement character
sanitize('my element', 'name', { replacement: '-' })  // 'my-element'

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Which production should I use?

Context	Production
XML element/attribute names (namespace-aware)	qName
SVG id attribute values	ncName
Namespace prefix alone	ncName
DOCTYPE <!ENTITY name ...>	name
DOCTYPE <!NOTATION name ...>	name
DTD NMTOKEN attribute values	nmToken
DTD NMTOKENS attribute values	nmTokens

Note: DOCTYPE entity and notation names must use Name, not QName. Colons carry no namespace meaning in the DTD subset.

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API

name(str, opts?) → boolean

ncName(str, opts?) → boolean

qName(str, opts?) → boolean

nmToken(str, opts?) → boolean

nmTokens(str, opts?) → boolean

opts:

• xmlVersion: '1.0' (default) | '1.1'
• asciiOnly: boolean (default false) — ASCII-only fast path, see above

createValidator(production, opts?) → memoized (str) => boolean, with .reset()

opts:

• xmlVersion: '1.0' (default) | '1.1'
• asciiOnly: boolean (default false)
• maxCacheSize: number (default 2048) — cache stops accepting new entries once reached; existing entries keep serving hits

validate(str, production, opts?) → ValidationResult

production: 'name' | 'ncName' | 'qName' | 'nmToken' | 'nmTokens'

opts: same as boolean validators (xmlVersion, asciiOnly)

validateAll(strings[], production, opts?) → ValidationResult[]

opts: same as validate

sanitize(str, production?, opts?) → string

opts:

• xmlVersion: '1.0' | '1.1'
• replacement: string (default '_')
• asciiOnly: boolean (default false) — also replaces non-ASCII characters, not just XML-illegal ones

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License

MIT