in tools/gen_valid_chars.cc [6:15]
void dump_array(std::ostream& os, const std::string& name, const std::array<bool, 256>& chars) {
os << "static constexpr std::array<bool, 256> " << name << " = {{";
os << chars[0];
for (auto i = 1u; i < chars.size(); ++i) {
os << ", " << chars[i];
}
os << "}};\n";
}