 
 (defcustom latex-unicode-math-mode-rules-extra
   nil
-  "Extra rules for `latex-unicode-math-mode'."
+  "Extra rules for `latex-unicode-math-mode'.
+Please add your own rules here."
   :type '(repeat (list :tag "Rule"
                        (string :tag "Input")
                        (choice :tag "Output" string character)))

    ("\\Phi" ?Φ)
    ("\\Psi" ?Ψ)
    ("\\Omega" ?Ω))
  "Greek letters for `latex-unicode-math-mode'."
  :type '(repeat (list :tag "Rule"
                       (string :tag "Input")
                       (choice :tag "Output" string character)))

    ("\\cdots" ?⋯)
    ("..." "…")
    ("\\ldots" ?…)
    )
  "Generic rules for `latex-unicode-math-mode'.
Superscripts are not declared because they conflict with ' in
math mode.  In particular, I do not know how to handle $X'²$.
With \\DeclareUnicodeCharacter{00B2}{^2} LaTeX gives a \"Double
superscript\" error.  The prime character ' is an active
character and uses \\futurelet trickery to avoid the double
superscript error in $X'^2$.

Subscripts don't look good in my font, so we omit them for now."
  :type '(repeat (list :tag "Rule"
                       (string :tag "Input")
                       (choice :tag "Output" string character)))
