improve docs

Author: nitely

src/regex.nim

@@ -283,6 +283,32 @@ the scope, and it contains the submatches for every capture group.
       matched = true
     doAssert matched
 
+Bad UTF-8 input text
+####################
+
+This lib makes no effort to handle bad/malformed UTF-8 input text.
+The behaviour on bad input is currently undefined, and it will
+likely result in an internal AssertionDefect or some other error.
+
+What can be done about this is validating the input text before
+passing it to the match function.
+
+.. code-block:: nim
+    :test:
+    import unicode
+    # good input text
+    doAssert validateUtf8("abc") == -1
+    # bad input text
+    doAssert validateUtf8("\xf8\xa1\xa1\xa1\xa1") != -1
+
+Match binary data
+#################
+
+Matching on arbitrary binary data (i.e: not utf-8) is not currently supported.
+Both the regex and the input text are assumed to be valid utf-8.
+The input text is treated as utf-8, and setting the regex to ASCII mode
+won't help.
+
 ]##
 
 import std/tables