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.

signature S = sig
    type t
    val x : t
end

signature T = sig
    structure M : S

    type u
    val y : u

    structure N : S
end

structure M : T = struct
    structure M = struct
        val x = True
    end

    val y = 0

    structure N = struct
        val x = "hi"
    end
end