docs: add module-level docstring to validator.py

cve_bin_tool/validator.py

@@ -5,6 +5,25 @@
 
 from cve_bin_tool.log import LOGGER
 
+"""
+Validation utilities for CVE Binary Tool.
+
+This module provides functions to validate common security-related
+artifacts against their official XML schema definitions, including:
+
+- SPDX: Software Package Data Exchange documents
+- CycloneDX: Bill of Materials (SBOM) documents
+- SWID: Software Identification Tag files
+- Maven POM: Project Object Model files
+
+All functions delegate to a shared `_validate_xml` helper that applies
+the correct schema using the `xmlschema` library. Validation results are
+logged through the project’s logger for debugging and traceability.
+
+These helpers are used internally to ensure that inputs conform to
+standards before further analysis.
+"""
+
 # This downgrades a message during module loading.
 if True:  # Strange construction for pep8 compliance.
     logging.getLogger("xmlschema").setLevel(logging.WARNING)