prohibit /, #, and + from unquoted strings

because the spec proposes syntactic meanings for these

SPEC.md

@@ -102,8 +102,8 @@ Different from JSON:
    (details below)
  - String values may sometimes omit quotes.
     - Unquoted strings may not contain '$', '"', '{', '}',
-      '[', ']', ':', '=', ',', or '\' (backslash) and may not
-      contain whitespace (including newlines).
+      '[', ']', ':', '=', ',', '+', '#', '/' or '\' (backslash)
+      and may not contain whitespace (including newlines).
     - Unquoted strings do not support any form of escaping; the
       characters are all left as-is. If you need to use special
       characters or escaping, you have to quote the string.

src/main/java/com/typesafe/config/impl/Tokenizer.java

@@ -182,7 +182,7 @@ final class Tokenizer {
         // chars JSON allows to be part of a number
         static final String numberChars = "0123456789eE+-.";
         // chars that stop an unquoted string
-        static final String notInUnquotedText = "$\"{}[]:=,\\";
+        static final String notInUnquotedText = "$\"{}[]:=,\\+#/";
 
         // The rules here are intended to maximize convenience while
         // avoiding confusion with real valid JSON. Basically anything

src/test/scala/com/typesafe/config/impl/TestUtils.scala

@@ -133,7 +133,11 @@ abstract trait TestUtils {
         """{ "a" : { "c" : 2 }, "b" : y${a}z }""", // trying to interpolate an object in a string
         """{ "a" : ${a} }""", // simple cycle
         """[ { "a" : 2, "b" : ${${a}} } ]""", // nested substitution
-        "[ = ]", // = is not a valid token
+        "[ = ]", // = is not a valid token in unquoted text
+        "[ + ]",
+        "[ / ]",
+        "[ # ]",
+        "[ \\ ]",
         "{ include \"bar\" : 10 }", // include with a value after it
         "{ include foo }", // include with unquoted string
         "{ include : { \"a\" : 1 } }", // include used as unquoted key