How to produce unicode copyable alternative text? (with accsupp)

In the following example, I can't manage to make accsupp store the unicode alternative text. The resulting PDF looks as expected but the copyable text is not the correct one. I tried this with different accsupp options: method=plain,...=escape, ...=pdfstringdef, and unicode. (accsupp manual is here). I tried with Acrobat 9.4.1 (Linux) and Evince. I am using LuaLaTeX to compile.

The idea is that when I select the equation in the next document the text ⅆa is copied. (In most cases only a gets copied.)

\documentclass{article}
\usepackage{fontspec}
\setmainfont{Cambria}
\usepackage{accsupp}
\setmathfont{Cambria Math}

\begin{document}

\BeginAccSupp{unicode,ActualText=ⅆa} %method=plain, ...=escape, ...=pdfstringdef
$da$
\EndAccSupp{}

\end{document}

-

Big chars (characters with more than 8 bits) of LuaTeX/XeTeX are not yet fully supported. Workaround:

\documentclass{article}
\usepackage{fontspec}
\usepackage{accsupp}

\usepackage{tikz}%\usepackage{pgfmath}
\usepackage{stringenc}
\usepackage{pdfescape}

\makeatletter
\newcommand*{\BeginAccSuppUnicode}[1]{%
\EdefSanitize\asu@str{#1}%
\edef\asu@str{%
\expandafter\expandafter\expandafter\asu@ToSpaceOther
\expandafter\asu@str\space\@nil
}%
\expandafter\let\expandafter\asu@str\expandafter\@empty
\expandafter\asu@ToHexUC\asu@str\relax
\EdefUnescapeHex{\asu@str}{\asu@str}%
\StringEncodingConvert{\asu@str}{\asu@str}{utf32be}{utf16be}%
\EdefEscapeHex{\asu@str}{\asu@str}%
\BeginAccSupp{%
unicode,%
method=hex,%
ActualText=\asu@str
}%
}
\begingroup
\lccode\9=\ %
\lowercase{\endgroup
\def\asu@SpaceOther{9}%
}
\def\asu@ToSpaceOther#1 #2\@nil{%
#1%
\ifx\\#2\\%
\expandafter\@gobble
\else
\asu@SpaceOther
\expandafter\@firstofone
\fi
{\asu@ToSpaceOther#2\@nil}%
}
\def\asu@ToHexUC#1{%
\ifx#1\relax
\else
\pgfmathHex{\the\numexpr#1+"10000000\relax}%
\edef\asu@str{%
\asu@str
0\expandafter\@gobble\pgfmathresult
}%
\expandafter\asu@ToHexUC
\fi
}
\makeatother

\begin{document}

\BeginAccSuppUnicode{ⅆa}
$da$
\EndAccSupp{}

\end{document}

-
mmm, I get this ! Undefined control sequence. // l.108 \pgfkeys with LuaLatex Version beta-0.76.0-2013122811 (TeX Live 2014/dev) (rev 4627). – alfC Apr 14 '14 at 5:38
".. are not fully supported yet" by who? by accsupp or by xe/lualatex? – alfC Apr 14 '14 at 5:40
@alfC: Try with \usepackge{tikz}. There might be an issue with missing module dependencies of pgf/TIkZ, because the code only uses \pgfmathHex. – Heiko Oberdiek Apr 14 '14 at 5:46
@alfC: For example, packages stringenc and pdfescape, accsupp could be updated to support "big chars". A clear and unambiguous specification for the support of "big chars" is probably the most difficult part. – Heiko Oberdiek Apr 14 '14 at 5:50
@alfC: For example, you can't use \verb inside an argument. The package just provides the basics, but onthe other hand, it supports different formats including plain TeX. Thus, just make a nice cozy command. e.g. something like \newcommmand{\accsupp}[2]{\BeginAccSupp{<options>,ActualText={#1}}#2\EndAccSupp‌​{}}` which hides the option settings from the user interface. – Heiko Oberdiek Apr 14 '14 at 10:31