+fun yourDomainHost s =
+ yourDomain s
+ orelse let
+ val (pref, suf) = Substring.splitl (fn ch => ch <> #".") (Substring.full s)
+ in
+ Substring.size suf > 0
+ andalso validHost (Substring.string pref)
+ andalso yourDomain (Substring.string
+ (Substring.slice (suf, 1, NONE)))
+ end
+
+fun validUser s = size s > 0 andalso size s < 20
+ andalso CharVector.all Char.isAlphaNum s
+
+val validGroup = validUser
+
+val _ = Env.type_one "no_spaces"
+ Env.string
+ (CharVector.all (fn ch => not (Char.isSpace ch)))
+val _ = Env.type_one "no_newlines"
+ Env.string
+ (CharVector.all (fn ch => ch <> #"\n" andalso ch <> #"\r"))
+