This trigger type can be used to intercept a player attempting to practice
    with the recipient mobile. The following variables are set:

    @teacher - The mobile that owns the script.

    @student - The mobile attempting to practice with the @teacher.

    @mode    - The mode in which the @student invoked the practice command.
               This will have a value of either "list" or "learn" depending on
               whether the student wants the list of skills taught by the
               teacher or whether they are actually trying to practice a
               skill.

    @skill   - The name of the skill the @student is attempting to learn
               (if any).

    @skillId - The numerical ID of the skill the @student is attempting to
               learn (if any).


    If the script returns a non-zero value then the attempt to practice will
    be considered handled by the internal engine. In other other words, no
    further handling will be done internally.

    Example:

    protect
    {
        if( %getRace( @student ) == Troll )
        {
            talk @student I don't teach dirty trolls such as yourself!

            //
            // The "retval" statement returns a value but does NOT exit
            // the script.
            //
            retval 1

            wait 3 secs
            kill @student
        }
        endif
    }
    endprotect