[NTG-context] move glyph vertically

[Pablo Rodriguez]

Dear list,

I have the following sample:

  \startluacode
       fonts.handlers.otf.addfeature {
           name = "gpos_test",
           type = "single",
           data = {
                 [ '¿' ] = 1000,
                 [ '¡' ] = 1000,
           }
       }
  \stopluacode
  \definefontfeature[ktest][gpost_tes=yes]

  \starttext
  \startTEXpage[offset=1em]
  \feature[+][gpos_test]
  ¿? ¡!
  \stopTEXpage
  \stoptext

This tries to move vertically the opening question and exclamation
marks, so they are at the same height that its closing counterparts.

I thought there may be a GPOS feature that could achieve this, but I
must admit I have no idea about how to achive it.

In my document, this should only work with the slanted feature.

Could anyone tell me how could I move vertically single glyphs?

Many thanks for your help,

Pablo