Function xmlParserValidityWarning 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn xmlParserValidityWarning(
    ctx: *mut c_void,
    msg: *const c_char,
)

Default validity warning handler — void xmlParserValidityWarning(void *ctx, const char *msg, ...).

SAFETY

• ctx must be valid pointers (or NULL where the upstream C contract allows), obtained from the matching constructor/owner and not yet freed; the callee may take or keep ownership exactly as the C API specifies.

• msg must point to valid NUL-terminated strings (or NULL where the C contract allows) for the lifetime of the call.

The caller must not race this call with concurrent mutation of the same objects from other threads (per-object state is not internally synchronized). Violating any of the above is undefined behavior.

Exercised by the C-API differential courts (courts/suites/data-abi/*-family-probe.c) and the CLI differential courts; those pass byte-for-byte against the upstream oracle.