Unify filter regular expression, disallow spaces, add optional word.

assets/javascripts/discourse/components/tag-chooser.js.es6

@@ -26,7 +26,9 @@ export default Ember.TextField.extend({
   }.observes('value'),
 
   _initializeTags: function() {
-    var site = this.site;
+    var site = this.site,
+        filterRegexp = new RegExp(this.site.tags_filter_regexp, "g");
+
     this.$().select2({
       tags: true,
       placeholder: I18n.t('tagging.choose_for_topic'),
@@ -53,7 +55,7 @@ export default Ember.TextField.extend({
         callback(data);
       },
       createSearchChoice: function(term, data) {
-        term = term.replace(/[<\\\/\>\.\#\?\&]/g, '').trim();
+        term = term.replace(filterRegexp, '').trim();
 
         // No empty terms, make sure the user has permission to create the tag
         if (!term.length || !site.get('can_create_tag')) { return; }

config/locales/client.en.yml

@@ -20,5 +20,5 @@ en:
     tagging:
       all_tags: "All Tags"
       tags: "Tags"
-      choose_for_topic: "choose tags for this topic"
+      choose_for_topic: "choose tags for this topic (optional)"
       topics_tagged: "Topics tagged <span class='discourse-tag'>{{tag}}</span>"

plugin.rb

@@ -5,6 +5,7 @@
 
 after_initialize do
   TAGS_FIELD_NAME = "tags"
+  TAGS_FILTER_REGEXP = /[<\\\/\>\.\#\?\&\s]/
 
   module ::DiscourseTagging
     class Engine < ::Rails::Engine
@@ -85,7 +86,7 @@ def self.tags_by_count(limit=nil)
 
     if params['tags'].present?
       tags = params['tags']
-      tags.map! {|t| t.downcase.strip[0...SiteSetting.max_tag_length].gsub(/[<\\\/\>\.\#\?\&]/, '') }
+      tags.map! {|t| t.downcase.strip[0...SiteSetting.max_tag_length].gsub(TAGS_FILTER_REGEXP, '') }
       tags.delete_if {|t| t.blank? }
       tags.uniq!
 
@@ -112,6 +113,7 @@ def self.tags_by_count(limit=nil)
   end
 
   add_to_serializer(:site, :can_create_tag) { scope.can_create_tag? }
+  add_to_serializer(:site, :tags_filter_regexp) { TAGS_FILTER_REGEXP.source }
 
   module AddCanCreateTagToGuardian
     def can_create_tag?