/usr/include/boost/regex/ is in libboost1.62-dev 1.62.0+dfsg-5.
This file is owned by root:root, with mode 0o755.
..
/usr/include/boost/regex/concepts.hpp
/usr/include/boost/regex/config/
/usr/include/boost/regex/config.hpp
/usr/include/boost/regex/config/borland.hpp
/usr/include/boost/regex/config/cwchar.hpp
/usr/include/boost/regex/icu.hpp
/usr/include/boost/regex/mfc.hpp
/usr/include/boost/regex/pattern_except.hpp
/usr/include/boost/regex/pending/
/usr/include/boost/regex/pending/object_cache.hpp
/usr/include/boost/regex/pending/static_mutex.hpp
/usr/include/boost/regex/pending/unicode_iterator.hpp
/usr/include/boost/regex/regex_traits.hpp
/usr/include/boost/regex/user.hpp
/usr/include/boost/regex/v4/
/usr/include/boost/regex/v4/basic_regex.hpp
/usr/include/boost/regex/v4/basic_regex_creator.hpp
/usr/include/boost/regex/v4/basic_regex_parser.hpp
/usr/include/boost/regex/v4/c_regex_traits.hpp
/usr/include/boost/regex/v4/char_regex_traits.hpp
/usr/include/boost/regex/v4/cpp_regex_traits.hpp
/usr/include/boost/regex/v4/cregex.hpp
/usr/include/boost/regex/v4/error_type.hpp
/usr/include/boost/regex/v4/fileiter.hpp
/usr/include/boost/regex/v4/instances.hpp
/usr/include/boost/regex/v4/iterator_category.hpp
/usr/include/boost/regex/v4/iterator_traits.hpp
/usr/include/boost/regex/v4/match_flags.hpp
/usr/include/boost/regex/v4/match_results.hpp
/usr/include/boost/regex/v4/mem_block_cache.hpp
/usr/include/boost/regex/v4/perl_matcher.hpp
/usr/include/boost/regex/v4/perl_matcher_common.hpp
/usr/include/boost/regex/v4/perl_matcher_non_recursive.hpp
/usr/include/boost/regex/v4/perl_matcher_recursive.hpp
/usr/include/boost/regex/v4/primary_transform.hpp
/usr/include/boost/regex/v4/protected_call.hpp
/usr/include/boost/regex/v4/regbase.hpp
/usr/include/boost/regex/v4/regex.hpp
/usr/include/boost/regex/v4/regex_format.hpp
/usr/include/boost/regex/v4/regex_fwd.hpp
/usr/include/boost/regex/v4/regex_grep.hpp
/usr/include/boost/regex/v4/regex_iterator.hpp
/usr/include/boost/regex/v4/regex_match.hpp
/usr/include/boost/regex/v4/regex_merge.hpp
/usr/include/boost/regex/v4/regex_raw_buffer.hpp
/usr/include/boost/regex/v4/regex_replace.hpp
/usr/include/boost/regex/v4/regex_search.hpp
/usr/include/boost/regex/v4/regex_split.hpp
/usr/include/boost/regex/v4/regex_token_iterator.hpp
/usr/include/boost/regex/v4/regex_traits.hpp
/usr/include/boost/regex/v4/regex_traits_defaults.hpp
/usr/include/boost/regex/v4/regex_workaround.hpp
/usr/include/boost/regex/v4/states.hpp
/usr/include/boost/regex/v4/sub_match.hpp
/usr/include/boost/regex/v4/syntax_type.hpp
/usr/include/boost/regex/v4/u32regex_iterator.hpp
/usr/include/boost/regex/v4/u32regex_token_iterator.hpp
/usr/include/boost/regex/v4/w32_regex_traits.hpp