I have lua code that generates this for METAPOST:

ApplicationComponentLogo( w, h, "withcolor (0.686,1.000,1.000) withtransparency (1,0.200)", "withcolor (0.000,0.000,0.000) withtransparency (1,1.000) withpen pencircle scaled 1.000", "\{Hello\}, "&ditto&"(a)"&ditto&" [World]!") shifted (x, -y); draw pic;

The string to be typeset, eventually is this: 

{Hello}, "(a)" [World]!

So, with double quotes in the string. The function creating the actual string to pass to METAPOST (above) is this:

local function mpLabelString( xmlLabelString)
  -- Returns a string where each " is replaced by a METAPOST compatible result, except for outer double quotes"
  rep = {
      [1] = { "\"", "\"&ditto&\""   },
  }
  local tmpString = string.formatters( "%!tex!", xmlLabelString)
  return lpeg.replacer(rep):match(tmpString)
end

That works. Then, in METAPOST the vardef ‘ApplicationComponentLogo’  calls a vardef makeTeXLabel 

draw makeTeXLabel( w, h, name) shifted (w/2,0);

which, for now, simplified does this:

vardef makeTeXLabel( expr w, h, name) =
  save p; picture p ;
  save s; string s;
  s := "\framed{" & name & "}”;
  % s := "\type-" & name & "-";
  p := textext( s);
  p
enddef;

But, this is what is in string s before it is sent to textext():

\framed {{Hello}, "(a)" [World]!}

In other words, the escapes on the curly braces are lost and now the curly braces are ignored by TeX. 

I tried adding a doubling of the backslahes to the replacement:

  rep = {
      [1] = { "\"", "\"&ditto&\""   },
      [2] = { "\\", "\\\\" },
  }

But then the string that is typeset (and given to textext()) becomes 

\framed {\\{Hello\\}, "(a)" [World]!}

And the result in the output is the same. No curly braces.

My route is probably to complex anyway, but what can I do for the curly braces to be actually typeset?

G