LibYAML parser error handling

I am using LibYAML for the first time, and I can't figure out how the
library reports parser errors to the application.

Looking at yaml.h, I can see the "Error Handling" members of struct
yaml_parser_s, but I also see:

   All members are internal.  Manage the structure using the
   yaml_parser_ family of functions.

But it don't see any yaml_parser_ functions that have anything to do
with error handling.  How then am I supposed to access these members?

If (contrary to what the header says), I am supposed to access these
members directly, how can I know when they contain usable information?

(Links to documentation happily accepted.  I haven't been able to find
anything about LibYAML error handling anywhere.)

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