The presence of this attribute allows the compiler to catch dangling references.

std::string_view has this annotation. we should follow suit.

"This ensures that constructing a StringPiece (StringData in our case) from a temporary (xvalue)
std::string will produce a compiler warning (error for us). And it
matches the annotation libc++ does for std::string_view."

https://bugs.chromium.org/p/chromium/issues/detail?id=1282468

class [[gsl::Pointer]] StringData {
...
};

https://godbolt.org/z/Kdoec79ar