Starting with "The C string library" made me instantly tune out. C has a standard library, which has some string-related functions. There is no "C string library".
Ultimately this file is supposed to be the one stop shop for all string related needs, so in what sense isn't that a library.
After all, what C has is "the C library". It's what standard literally calls it (it doesn't even explicitly provide for existence of other kinds of libraries) but everyone calls it "the standard library". Is it correct? Arguably, no.