Why can the std::sort receive a function object as one of its parameters?

Why can the std::sort receive a function object as one of its parameters?

• The std::sort function is a template. The programmer is free to enter the sorting algorithm in a function object as an argument.
• Actually, std::sort takes only one argument, which is the container to be sorted.
• std::sort operates on a template container. The compiler does not know how to relationally compare the values it contains, so a function must be provided to do the comparison.
• std::sort will use the parameter function as an error handler. The function will be called if an error occurs.