Add a section on Strings and Unicode

I'm not proud of wording but we need clarifications
on this subject.

arrays.dd

@@ -839,6 +839,28 @@ w = "\r"[0]; // w is assigned the carriage return wchar character
 d = 'd';     // d is assigned the character 'd'
 ---------
 
+$(H5 $(LNAME2 strings_unicode, Strings and Unicode))
+        $(P Note that built-in comparison operators operate on 
+        $(WEB www.unicode.org/glossary/#code_unit, code unit) basis. 
+        The end result for valid strings is the same as that of 
+        $(WEB www.unicode.org/glossary/#code_point, code point) 
+        for $(WEB www.unicode.org/glossary/#code_point, code point)
+        comparision as long as both strings are in the same
+        $(WEB www.unicode.org/glossary/#normalization_form, normalization form).
+        Since normalization is a costly operation not suitable for language 
+        primitives it's assumed to be enforced by the user.
+        )
+        $(P Standard library lends a hand for comparing strings with mixed encodings
+        (by transparently decoding, see $(PHOBOS algorithm, cmp, std.algorithm.cmp)), 
+        $(PHOBOS uni, icmp, case-insensitive comparision) and $(PHOBOS uni, normalize, normalization).
+        )
+        $(P The last but not least - a desired string sorting order differs 
+        by culture and language and is usually nothing like code point 
+        for code point comparison. The natural order of strings is obtained by applying
+        $(WEB www.unicode.org/reports/tr10/, unicode collation algorithm)
+        that should be implemented in the standard library.
+        )
+
 $(H5 $(LNAME2 printf, C's printf() and Strings))
 
         $(P $(D printf()) is a C function and is not part of D. $(D printf())
@@ -930,4 +952,5 @@ Macros:
         WIKI=Arrays
         CATEGORY_SPEC=$0
         FOO=
-
+        WEB=$(LINK2 http://$1, $2)
+        PHOBOS=<a href="phobos/std_$1.html#$2">$3</a>

doc.ddoc

@@ -485,6 +485,7 @@ REG=©
 H2=<h2>$0</h2>
 H3=<h3>$0</h3>
 H4=<h4>$0</h4>
+H5=<h5>$0</h5>
 CODE_LCURL=$(D {)
 CODE_RCURL=$(D })
 CODE_PERCENT=$(D %)