--- a/coffee/rivets.coffee	Mon Mar 21 21:46:23 2016 +0800
+++ b/coffee/rivets.coffee	Mon Mar 21 22:56:28 2016 +0800
@@ -12,6 +12,14 @@
     obj.set(keypath, value)
 
 
+rivets.formatters['only'] = (value, allowed...) ->
+  if value in allowed then value else ''
+
+
+rivets.formatters['eq'] = (a, b) ->
+  a is b
+
+
 rivets.formatters['format-date'] = (value, format) ->
   if value? then value.format(format) else ''
 

--- a/js/rivets.js	Mon Mar 21 21:46:23 2016 +0800
+++ b/js/rivets.js	Mon Mar 21 22:56:28 2016 +0800
@@ -1,5 +1,8 @@
 // Generated by CoffeeScript 1.10.0
 (function() {
+  var slice = [].slice,
+    indexOf = [].indexOf || function(item) { for (var i = 0, l = this.length; i < l; i++) { if (i in this && this[i] === item) return i; } return -1; };
+
   rivets.adapters[':'] = {
     observe: function(obj, keypath, callback) {
       return obj.on('change:' + keypath, callback);
@@ -15,6 +18,20 @@
     }
   };
 
+  rivets.formatters['only'] = function() {
+    var allowed, value;
+    value = arguments[0], allowed = 2 <= arguments.length ? slice.call(arguments, 1) : [];
+    if (indexOf.call(allowed, value) >= 0) {
+      return value;
+    } else {
+      return '';
+    }
+  };
+
+  rivets.formatters['eq'] = function(a, b) {
+    return a === b;
+  };
+
   rivets.formatters['format-date'] = function(value, format) {
     if (value != null) {
       return value.format(format);

--- a/js/rivets.js.map	Mon Mar 21 21:46:23 2016 +0800
+++ b/js/rivets.js.map	Mon Mar 21 22:56:28 2016 +0800
@@ -6,5 +6,5 @@
     "coffee/rivets.coffee"
   ],
   "names": [],
-  "mappings": ";AAAA;EAAA,MAAM,CAAC,QAAS,CAAA,GAAA,CAAhB,GACE;IAAA,OAAA,EAAS,SAAC,GAAD,EAAM,OAAN,EAAe,QAAf;aACP,GAAG,CAAC,EAAJ,CAAO,SAAA,GAAY,OAAnB,EAA4B,QAA5B;IADO,CAAT;IAGA,SAAA,EAAW,SAAC,GAAD,EAAM,OAAN,EAAe,QAAf;aACT,GAAG,CAAC,GAAJ,CAAQ,SAAA,GAAY,OAApB,EAA6B,QAA7B;IADS,CAHX;IAMA,GAAA,EAAK,SAAC,GAAD,EAAM,OAAN;aACH,GAAG,CAAC,GAAJ,CAAQ,OAAR;IADG,CANL;IASA,GAAA,EAAK,SAAC,GAAD,EAAM,OAAN,EAAe,KAAf;aACH,GAAG,CAAC,GAAJ,CAAQ,OAAR,EAAiB,KAAjB;IADG,CATL;;;EAaF,MAAM,CAAC,UAAW,CAAA,aAAA,CAAlB,GAAmC,SAAC,KAAD,EAAQ,MAAR;IACjC,IAAG,aAAH;aAAe,KAAK,CAAC,MAAN,CAAa,MAAb,EAAf;KAAA,MAAA;aAAyC,GAAzC;;EADiC;;EAInC,MAAM,CAAC,UAAW,CAAA,UAAA,CAAlB,GAAgC,SAAC,KAAD;IAC9B,IAAG,aAAH;aAAe,KAAK,CAAC,WAAN,CAAA,EAAf;KAAA,MAAA;aAAwC,GAAxC;;EAD8B;;EAIhC,MAAM,CAAC,UAAW,CAAA,UAAA,CAAlB,GAAgC,SAAC,KAAD;IAC9B,IAAG,aAAH;aAAe,KAAK,CAAC,OAAN,CAAA,EAAf;KAAA,MAAA;aAAoC,GAApC;;EAD8B;AAtBhC"
+  "mappings": ";AAAA;AAAA,MAAA;;;EAAA,MAAM,CAAC,QAAS,CAAA,GAAA,CAAhB,GACE;IAAA,OAAA,EAAS,SAAC,GAAD,EAAM,OAAN,EAAe,QAAf;aACP,GAAG,CAAC,EAAJ,CAAO,SAAA,GAAY,OAAnB,EAA4B,QAA5B;IADO,CAAT;IAGA,SAAA,EAAW,SAAC,GAAD,EAAM,OAAN,EAAe,QAAf;aACT,GAAG,CAAC,GAAJ,CAAQ,SAAA,GAAY,OAApB,EAA6B,QAA7B;IADS,CAHX;IAMA,GAAA,EAAK,SAAC,GAAD,EAAM,OAAN;aACH,GAAG,CAAC,GAAJ,CAAQ,OAAR;IADG,CANL;IASA,GAAA,EAAK,SAAC,GAAD,EAAM,OAAN,EAAe,KAAf;aACH,GAAG,CAAC,GAAJ,CAAQ,OAAR,EAAiB,KAAjB;IADG,CATL;;;EAaF,MAAM,CAAC,UAAW,CAAA,MAAA,CAAlB,GAA4B,SAAA;AAC1B,QAAA;IAD2B,sBAAO;IAClC,IAAG,aAAS,OAAT,EAAA,KAAA,MAAH;aAAyB,MAAzB;KAAA,MAAA;aAAoC,GAApC;;EAD0B;;EAI5B,MAAM,CAAC,UAAW,CAAA,IAAA,CAAlB,GAA0B,SAAC,CAAD,EAAI,CAAJ;WACxB,CAAA,KAAK;EADmB;;EAI1B,MAAM,CAAC,UAAW,CAAA,aAAA,CAAlB,GAAmC,SAAC,KAAD,EAAQ,MAAR;IACjC,IAAG,aAAH;aAAe,KAAK,CAAC,MAAN,CAAa,MAAb,EAAf;KAAA,MAAA;aAAyC,GAAzC;;EADiC;;EAInC,MAAM,CAAC,UAAW,CAAA,UAAA,CAAlB,GAAgC,SAAC,KAAD;IAC9B,IAAG,aAAH;aAAe,KAAK,CAAC,WAAN,CAAA,EAAf;KAAA,MAAA;aAAwC,GAAxC;;EAD8B;;EAIhC,MAAM,CAAC,UAAW,CAAA,UAAA,CAAlB,GAAgC,SAAC,KAAD;IAC9B,IAAG,aAAH;aAAe,KAAK,CAAC,OAAN,CAAA,EAAf;KAAA,MAAA;aAAoC,GAApC;;EAD8B;AA9BhC"
 }
\ No newline at end of file