/usr/include/sbml/validator/ is in libsbml5-dev 5.13.0+dfsg-1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/sbml/validator/ConsistencyValidator.h
/usr/include/sbml/validator/ConstraintMacros.h
/usr/include/sbml/validator/IdentifierConsistencyValidator.h
/usr/include/sbml/validator/InternalConsistencyValidator.h
/usr/include/sbml/validator/L1CompatibilityValidator.h
/usr/include/sbml/validator/L2v1CompatibilityValidator.h
/usr/include/sbml/validator/L2v2CompatibilityValidator.h
/usr/include/sbml/validator/L2v3CompatibilityValidator.h
/usr/include/sbml/validator/L2v4CompatibilityValidator.h
/usr/include/sbml/validator/L3v1CompatibilityValidator.h
/usr/include/sbml/validator/MathMLConsistencyValidator.h
/usr/include/sbml/validator/ModelingPracticeValidator.h
/usr/include/sbml/validator/OverdeterminedValidator.h
/usr/include/sbml/validator/SBMLExternalValidator.h
/usr/include/sbml/validator/SBMLInternalValidator.h
/usr/include/sbml/validator/SBMLValidator.h
/usr/include/sbml/validator/SBOConsistencyValidator.h
/usr/include/sbml/validator/StrictUnitConsistencyValidator.h
/usr/include/sbml/validator/UnitConsistencyValidator.h
/usr/include/sbml/validator/VConstraint.h
/usr/include/sbml/validator/Validator.h