Function validateQName

xml/_common.ts:420–441

(name: string, colonIndex: number)

 * @returns Error message if invalid, null if valid.
 */
export function validateQName(name: string, colonIndex: number): string | null {
  if (colonIndex === -1) {
    return null; // No colon means valid NCName (already validated by name char rules)
  }

  // Colon at start (:foo) - invalid
  if (colonIndex === 0) {
    return "QName cannot start with ':'";
  }

  // Colon at end (foo:) - invalid
  if (colonIndex === name.length - 1) {
    return "QName cannot end with ':'";
  }

  // Multiple colons (a:b:c) - invalid
  if (name.indexOf(":", colonIndex + 1) !== -1) {
    return "QName cannot contain multiple ':'";
  }

  return null; // Valid QName
}

/**
 * Validates a namespace binding (xmlns or xmlns:prefix attribute).