a string, or NULL. [allow-none]
a stream of data, or NULL. [allow-none][array length=data_size]
return location for the certainty of the result, or NULL. [allow-none]out
a string indicating a guessed content type for the given data. Free with g_free()
Guesses the content type based on example data. If the function is uncertain, result_uncertain will be set to TRUE. Either filename or data may be NULL, in which case the guess will be based solely on the other argument.