/**
 * SchemaPreflight  (G42 — v1.5.0)
 * ──────────────────────────────────
 * Public API: validateSchema(xsdSource) → SchemaIssue[]
 *
 * Checks the XSD schema itself for internal consistency BEFORE it is used
 * for instance validation.  Surfaces errors at schema-load time rather than
 * at first validation call.
 *
 * Checks performed
 * ────────────────
 *  1. Undefined type references  (element/attribute typeName not in schema)
 *  2. Circular type definitions   (type A extends B extends A)
 *  3. Invalid derivations         (extending a 'final' type)
 *  4. Conflicting element declarations (same qualified name, different types)
 *  5. xs:keyref → xs:key linkage  (keyref references a non-existent key)
 *  6. Undefined element/attribute ref="" references
 *
 * Usage
 * ─────
 *  import { validateSchema } from 'xml-xsd-engine';
 *  const issues = validateSchema(xsdSource);
 *  // [{ severity: 'error', code: 'SCHEMA_UNDEFINED_REF', message: '...' }]
 */
import { SchemaModel } from '../schema/SchemaModel';
import { XmlErrorCode } from '../errors/XmlError';
export type SchemaSeverity = 'error' | 'warning' | 'info';
export interface SchemaIssue {
    severity: SchemaSeverity;
    /** Stable error code (G37) */
    code: XmlErrorCode;
    /** Human-readable description */
    message: string;
    /** The schema component name involved (element, type, constraint…) */
    component?: string;
}
/**
 * Parse and validate a schema source string, returning a list of schema-level
 * issues.  Returns an empty array if the schema is self-consistent.
 *
 * Throws only if the source cannot be parsed at all (i.e. is not valid XML).
 */
export declare function validateSchema(xsdSource: string): SchemaIssue[];
/**
 * Run preflight checks on an already-parsed SchemaModel.
 * Useful when you have loaded the schema via parseXsdAsync or from cache.
 */
export declare function checkSchema(model: SchemaModel): SchemaIssue[];
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