Question: Maple special_primes

I am trying to understand how maple "isprime" algorithm works. But I can't find anywhere what special_primes means.

 showstat(isprime);

isprime := proc(n)
local btor, nr, p, r;
   1   if not type(n,'integer') then
   2     if type(n,('complex')('numeric')) then
   3       error "argument must be an integer"
         else
   4       return 'isprime(n)'
         end if
       end if;
   5   if n < 2 then
   6     return false
       elif member(n,isprime:-special_primes) then
   7     return true
       elif igcd(2305567963945518424753102147331756070,n) <> 1 then
   8     return false
       elif n < 10201 then
   9     return true
       elif igcd(8496969489233418110532339909187349965926062586648932736611545426342203893270769390909069477309509137509786917118668028861499333825097682386722983737962963066757674131126736578936440788157186969893730633113066478620448624949257324022627395437363639038752608166758661255956834630697220447512298848222228550062683786342519960225996301315945644470064720696621750477244528915927867113,n) <> 1 then
  10     return false
       elif n < 1018081 then
  11     return true
       else
  12     r := gmp_isprime(n);
  13     if not r or n <= 5000000000 then
  14       return r
         end if;
  15     nr := igcd(408410100000,n-1);
  16     nr := igcd(nr^5,n-1);
  17     r := iquo(n-1,nr);
  18     btor := modp(('power')(2,r),n);
  19     if cyclotest(n,btor,2,r) = false or irem(nr,3) = 0 and cyclotest(n,btor,3,r) = false or irem(nr,5) = 0 and cyclotest(n,btor,5,r) = false or irem(nr,7) = 0 and cyclotest(n,btor,7,r) = false then
  20       return false
         end if;
  21     if isqrt(n)^2 = n then
  22       return false
         end if;
  23     for p from 3 while numtheory:-jacobi(p^2-4,n) <> -1 do
  24       NULL
         end do;
  25     return evalb(TraceModQF(p,n+1,n) = [2, p])
       end if
end proc