Auto selecting optical sizes for a font

[Andres Conrado Montoya <andresconrado@gmail.com>]

Hello friends.
I'm trying to design a book using the typescript you can find at the
end of this message. I'm using the beautiful EBGaramond fonts from
Georg Duffner (http://www.georgduffner.at/ebgaramond/). This font
provides optical sizes to be used in different sizes (named "12" for
10.1pt or more, and "8" for 10 or less. These fonts automatically work
as expected in latex, thanks to a recent package included in CTAN
(ebgaramond package), selecting the correct font for the appropriate
size. However, the typescript I'm using selects the "8" size for
everything, without taking the type size into consideration. Is there
any way to make ConTeXt do this automatic selection of fonts regarding
of type size? I'm using version 2013.06.10 22:51.

Here is my example:

%%%%%%%%%%%%%%%%%%%%%%%%%%%
\enableregime[utf-8]
\mainlanguage[es]
\setupcapitals[sc=yes]

\definefontfeature[default][default]
[mode=node,calt=yes,liga=yes,dlig=yes,hlig=yes,ccmp=yes,kern=yes,mark=yes,mkmk=yes,onum=yes,pnum=yes,salt=yes,size=yes,expansion=quality,protrusion=quality]

\definefontfeature[smallcaps][smallcaps]
[mode=node,script=latn,smcp=yes,c2sc=yes,calt=yes,liga=yes,dlig=yes,hlig=yes,ccmp=yes,kern=yes,mark=yes,mkmk=yes,onum=yes,pnum=yes,salt=yes,size=yes,expansion=quality,protrusion=quality]

\starttypescript[serif][ebgaramond]
  \setups[font:fallback:serif]
  \definefontsynonym [EBGaramond-Regular]    [name:EBGaramond-Regular]
  \definefontsynonym [EBGaramond-Italic]     [name:EBGaramond-Italic]
\stoptypescript

\starttypescript[serif][ebgaramond]
  \definefontsynonym [Serif]           [EBGaramond-Regular]
[features=default]
  \definefontsynonym [SerifItalic]     [EBGaramond-Italic]
[features=default]
  \definefontsynonym [SerifCaps]       [Serif]
[features=smallcaps]
\stoptypescript

\definetypeface[ebg][rm][serif][ebgaramond][default]
\setupbodyfont[ebg,12pt]
\setupbodyfontenvironment[default][em=italic]

\setupinterlinespace[line=3.2ex]

\setupalign[lesshyphenation,hz,hanging]
\doublehyphendemerits=30000
\setupspacing[packed]

\starttext
\showframe
\showgrid

\input tufte
\stoptext
%%%%%%%%%%%%%%%%%%%%%%%%%%%


Thank so much for all your good work and help. :)
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