Function validateNamespaceBinding

xml/_common.ts:456–503

(
  attrName: string,
  attrValue: string,
  xml11: boolean,
)

 * @returns Error message if invalid, null if valid.
 */
export function validateNamespaceBinding(
  attrName: string,
  attrValue: string,
  xml11: boolean,
): string | null {
  const colonIndex = attrName.indexOf(":");
  const isDefaultNs = attrName === "xmlns";
  const prefix = isDefaultNs ? "" : attrName.slice(colonIndex + 1);
  const uri = attrValue;

  // xmlns: with empty local part is caught by QName validation
  // But check for empty prefix after xmlns:
  if (colonIndex !== -1 && prefix === "") {
    return "Cannot have empty namespace prefix after 'xmlns:'";
  }

  // Prefix unbinding: xmlns:foo="" is forbidden in NS 1.0, allowed in NS 1.1
  if (!isDefaultNs && uri === "" && !xml11) {
    return "Cannot unbind namespace prefix (empty URI) in Namespaces 1.0";
  }

  // Cannot declare xmlns prefix at all
  if (prefix === "xmlns") {
    return "Cannot declare the 'xmlns' prefix";
  }

  // xml prefix must use correct URI
  if (prefix === "xml" && uri !== XML_NAMESPACE) {
    return `Cannot bind 'xml' prefix to '${uri}': must use '${XML_NAMESPACE}'`;
  }

  // Only xml prefix can use xml namespace
  if (uri === XML_NAMESPACE && prefix !== "xml" && prefix !== "") {
    return `Cannot bind prefix '${prefix}' to '${XML_NAMESPACE}': only the 'xml' prefix may use this namespace`;
  }

  // Nothing can bind to xmlns namespace (includes default namespace case)
  if (uri === XMLNS_NAMESPACE) {
    return `Cannot bind any prefix to '${XMLNS_NAMESPACE}'`;
  }

  // Default namespace cannot be xml namespace
  if (isDefaultNs && uri === XML_NAMESPACE) {
    return `Cannot use '${XML_NAMESPACE}' as the default namespace`;
  }

  return null; // Valid binding
}

/**
 * Validates a PubidLiteral per XML 1.0 §2.3.