src/Pure/PIDE/command_span.scala

         case _: Command_Span =>
           (start /: content.iterator.takeWhile(tok => !tok.is_command))(_.advance(_))
         case _ => start
       }
 
-    def is_kind(keywords: Keyword.Keywords, pred: String => Boolean): Boolean =
+    def is_kind(keywords: Keyword.Keywords, pred: String => Boolean, other: Boolean): Boolean =
       keywords.kinds.get(name) match {
         case Some(k) => pred(k)
-        case None => false
+        case None => other
       }
 
     def is_begin: Boolean = content.exists(_.is_begin)
     def is_end: Boolean = content.exists(_.is_end)