add comment in xmpp_stringprep

src/common/xmpp_stringprep.py

@@ -162,9 +162,24 @@ def check_bidirectionals(self, string):
 
 
 class NamePrep:
-	""" Implements nameprep on international domain names.
-	
-	STD3ASCIIRules is assumed true in this implementation.
+	""" Implements preparation of internationalized domain names.
+
+		This class implements preparing internationalized domain names using the
+		rules defined in RFC 3491, section 4 (Conversion operations).
+
+		We do not perform step 4 since we deal with unicode representations of
+		domain names and do not convert from or to ASCII representations using
+		punycode encoding. When such a conversion is needed, the L{idna} standard
+		library provides the C{ToUnicode()} and C{ToASCII()} functions. Note that
+		L{idna} itself assumes UseSTD3ASCIIRules to be false.
+
+		The following steps are performed by C{prepare()}:
+
+			* Split the domain name in labels at the dots (RFC 3490, 3.1)
+			* Apply nameprep proper on each label (RFC 3491)
+			* Enforce the restrictions on ASCII characters in host names by
+				assuming STD3ASCIIRules to be true. (STD 3)
+			* Rejoin the labels using the label separator U+002E (full stop).
 	"""
 
 	# Prohibited characters.