documentation of \pdfgentounicode

[Karl Berry]

     /* s is a multiple value of form "uniXXXX" */
     /* s matched an entry with numeric value in the
        database, or a value derived from "uXXXX" */
     Imho this should be better documented.

Does this look right?

+Once a single \type{\pdfglyphtounicode} definition is made, whether it
+is used or not, another feature comes into play: glyph names of the form
+\type{uniXXXX} or \type{uXXXX} are mapped to the natural \type{U+XXXX}.
+Many fonts use this style of naming.

However, I guess I don't really understand. When I look at the pdf
resulting from running your example document, I do not see character
<30> (hex; aka 48 decimal, aka the "a") being mapped to the expected
U+1D44E (math italic small a), which seems to be what the font says to
do. There are other mappings for unused characters (I can't quite
understand where they are coming from). And running pdftotext generates
no output.

    That is quite nice and means that for example the libertine math
    font gets quite good tounicode values as it uses the uXXXX-syntax. 

How did you discern that the mapping is actually working? --thanks, karl.