This variable was flagged by a chromium check that looks for variables named like constants that end up in the `.data` ELF section (rather than in `.rodata`).
#define UPRV_ISDIGIT(c) (((c) >= '0') && ((c) <= '9'))
#define UPRV_ISALPHANUM(c) (uprv_isASCIILetter(c) || UPRV_ISDIGIT(c) )
-const char* kAttributeKey = "attribute";
+constexpr const char* kAttributeKey = "attribute";
static bool _isExtensionSubtags(char key, const char* s, int32_t len) {
switch (uprv_tolower(key)) {