Tignten up direction part of LANGDIR terminal.

Author: gkellogg

etc/n-triples.ebnf

@@ -10,7 +10,7 @@ quotedTriple      ::= '<<' subject predicate object '>>'
 
 IRIREF            ::=  '<' ([^#x00-#x20<>"{}|^`\] | UCHAR)* '>'
 BLANK_NODE_LABEL  ::= '_:' ( PN_CHARS_U | [0-9] ) ((PN_CHARS|'.')* PN_CHARS)?
-LANGDIR           ::= "@" [a-zA-Z]+ ( "-" [a-zA-Z0-9]+ )* ('--' ('ltr'|'rtl'))?`
+LANGDIR           ::= "@" [a-zA-Z]+ ( "-" [a-zA-Z0-9]+ )* ('--' [a-zA-Z]+)?`
 STRING_LITERAL_QUOTE ::= '"' ( [^#x22#x5C#xA#xD] | ECHAR | UCHAR )* '"'
 UCHAR             ::= ( "\u" HEX HEX HEX HEX )
                     | ( "\U" HEX HEX HEX HEX HEX HEX HEX HEX )

lib/rdf/ntriples/reader.rb

@@ -67,7 +67,7 @@ class Reader < RDF::Reader
 
     IRIREF               = /<((?:#{IRI_RANGE}|#{UCHAR})*)>/.freeze
     BLANK_NODE_LABEL     = /_:((?:[0-9]|#{PN_CHARS_U})(?:(?:#{PN_CHARS}|\.)*#{PN_CHARS})?)/.freeze
-    LANGDIR              = /@([a-zA-Z]+(?:-[a-zA-Z0-9]+)*(?:--[a-zA-Z0-9]+)?)/.freeze
+    LANGDIR              = /@([a-zA-Z]+(?:-[a-zA-Z0-9]+)*(?:--[a-zA-Z]+)?)/.freeze
     STRING_LITERAL_QUOTE = /"((?:[^\"\\\n\r]|#{ECHAR}|#{UCHAR})*)"/.freeze
 
     ST_START              = /^<</.freeze