src/Pure/Isar/token.scala

     source.startsWith(Symbol.open_decoded))
 
   def is_begin: Boolean = is_keyword && source == "begin"
   def is_end: Boolean = is_command && source == "end"
 
+  def is_begin_block: Boolean = is_command && source == "{"
+  def is_end_block: Boolean = is_command && source == "}"
+
   def content: String =
     if (kind == Token.Kind.STRING) Scan.Parsers.quoted_content("\"", source)
     else if (kind == Token.Kind.ALT_STRING) Scan.Parsers.quoted_content("`", source)
     else if (kind == Token.Kind.VERBATIM) Scan.Parsers.verbatim_content(source)
     else if (kind == Token.Kind.CARTOUCHE) Scan.Parsers.cartouche_content(source)