Add warning for bad characters when editing tiddler titles

Fixes #2351

core/language/en-GB/EditTemplate.multids

@@ -21,6 +21,7 @@ Tags/Add/Button: add
 Tags/Add/Placeholder: tag name
 Tags/Dropdown/Caption: tag list
 Tags/Dropdown/Hint: Show tag list
+Title/BadCharacterWarning: Warning: avoid using any of the characters <<bad-chars>> in tiddler titles
 Type/Dropdown/Caption: content type list
 Type/Dropdown/Hint: Show content type list
 Type/Delete/Caption: delete content type

core/ui/EditTemplate/title.tid

@@ -1,4 +1,18 @@
 title: $:/core/ui/EditTemplate/title
 tags: $:/tags/EditTemplate
 
-<$edit-text field="draft.title" class="tc-titlebar tc-edit-texteditor" focus="true"/>
+<$vars pattern="""[\|\[\]{}"]""" bad-chars="""`| [ ] { } " '`""">
+
+<$list filter="[is[current]regexp:draft.title<pattern>]" variable="listItem">
+
+<div class="tc-message-box">
+
+{{$:/language/EditTemplate/Title/BadCharacterWarning}}
+
+</div>
+
+</$list>
+
+</$vars>
+
+<$edit-text field="draft.title" class="tc-titlebar tc-edit-texteditor" focus="true"/>