//Declares an element "announcement"
//Containing the following sequence of elements
//distribution,head,more_info,courses
//Declares an element "course"
//Containing the following atributes (instructor=string,number=NMTOKEN)
//Declares an element "courses"
//Containing the following sequence of elements (course=unlimited number)
//Declares an element "distribution"
//Containing the following sequence of elements (to,from)
//With atribute (category=(string, required))
//Declares an element "from"
//Declares an element "head"
//Containing the following sequence of elements (subject,notice)
//Declares an element "courses"
//Containing the following sequence of elements (website=choice)
//Declares an element "courses"
//Declares an element "courses"
//Declares an element "courses"
//Declares an element "courses"