Return: a %NULL-terminated array of strings containing the ids of the available
style schemes or %NULL if no style scheme is available.
The array is sorted alphabetically according to the scheme name.
The array is owned by the @manager and must not be modified.
Returns the ids of the available style schemes.
Return: a %NULL-terminated array of strings containing the ids of the available style schemes or %NULL if no style scheme is available. The array is sorted alphabetically according to the scheme name. The array is owned by the @manager and must not be modified.