Function xmlIsLetter 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn xmlIsLetter(c: c_int) -> c_int

xmlIsLetter(int c) — BaseChar or Ideographic (parserInternals.c).

SAFETY

The function touches crate-global state only; it is safe as long as the caller respects the library’s global initialization/cleanup ordering (xmlInitParser before use, xmlCleanupParser only after all users are done).

Violating the global lifecycle ordering, or calling this after teardown or from a signal handler, is undefined behavior.