alertcondition() and highest() arguments

//@version=4
study("")
// Works as alertcondition() "message=" argument?
s1 = "kyky"                                 //  Y       s1 is compile time const string
s2 = input("ky")                            //      N   s2 is runtime input string
s3 = ""                                     //
s3 := s2 + s1                               //      N   s3 is mutable series string
s4 = close > open ? "yes" : s3              //      N   s4 is series string
s5 = s1 + s2                                //      N   s5 is runtime input string
s6 = s1 + "aaa"                             //  Y       s6 is compile time const string
s7 = s1 + tostring(10)                      //      N   s7 is compile time simple string
s8 = s1 + tostring(close)                   //      N   s8 is series string
alertcondition(true, "", s6)

// Works as highest() "length=" argument?
a1 = 1                                      //  Y       a1 is compile-time const int
a2 = input(2)                               //  Y       a2 is runtime input int
a3 = input(3)
a3 := a1 + a2                               //  Y       a3 is mutable series int
a4 = close > open ? 10 : 20                 //      N   a4 is series int
a5 = a1 + a2                                //  Y       a5 is runtime input int
a6 = a1 + 11                                //  Y       a6 is compile-time const int
plot(highest(a6))