Only emit extra T_SLASH tokens for "//".

lib/oga/xpath/lexer.rl

@@ -30,6 +30,13 @@ module Oga
       #
       AXIS_EMIT_NODE = %w{descendant-or-self parent self}
 
+      ##
+      # Axes that require an extra T_SLASH token to be emitted.
+      #
+      # @return [Array]
+      #
+      AXIS_EMIT_EXTRA_SLASH = %w{descendant-or-self}
+
       ##
       # @param [String] data The data to lex.
       #
@@ -246,7 +253,9 @@ module Oga
             add_token(:T_LPAREN)
             add_token(:T_RPAREN)
 
-            add_token(:T_SLASH) unless te == eof
+            if AXIS_EMIT_EXTRA_SLASH.include?(value) and te != eof
+              add_token(:T_SLASH)
+            end
           end
         }