Word description Pushes a formatted Lua string using an existing C variable argument list and returns its contents as a Factor string. On failure, Lua 5.5 pushes an error message and returns f. Uses the canonical va_list C type.
Notes On ARM64 a callback receives a borrowed cursor for its va_list parameter. Forwarding it to this function creates an independent native list position, so the same cursor may be forwarded repeatedly. Reading with va-arg advances the cursor before subsequent forwarding.
The cursor and its copies expire when the originating callback returns. Use them only on that callback's current Factor thread. The returned Factor string owns its contents and may be retained afterward.