Example in Bison's documentation

[guillaume marques]

Greetings all,

I have a little question regarding an example in the Bison's documentation.

In the Section 7.2 Lexical Tie-ins, how come the provided example does what
it is explained to do?

I understand the principle of the flags but I don't understand how Bison can
understand  when to parse the integer as an hexadecimal over an identifier
since we never say, when the flag is nonzero, that we should parse an 
hexadecimal,
and when it is zero, to parse an identifier.

I only see that the flags are set but not used.

Regards,

-- 
Guillaume Marques