Fix XML indentation in Emacs mode The return value of MATCH-STRING is a string. At least on Emacs 25, the comparisons between string and character with EQUAL could never succeed, and so the cases for matching braces were never triggered. GET-TEXT-PROPERTY may return a list rather than an atom (for example, on long lines with whitespace-mode turned on), and this broke the heuristic of looking for the tag face in previous text.

structure S = struct
        type t = int
        val x = 0

        structure S' : sig type u val y : t end = struct
                type u = t
                val y = x
        end

        signature Sig = sig
                type t
                val x : t
        end
end

open S.S'
open S
open S'

structure S' : Sig = S