In my version of Mac TextEdit (1.6), there is considerable though not complete access to OpenType features, and they can be controlled through the Typography panel from the Fonts panel.
I notice that Zapfino's many contextual alternates (e.g. changing /Z/a/p/f/i/n/o into the /Z_a_p_f_i_n_o glyph), which are programmed into the dlig feature, show up automatically, and can be turned off by deselecting "Special Ligatures."
Question one: How/why is "Special Ligatures" (e.g. dlig) turned on by default?--I would expect it to be off.
Question two: Why with the font I've designed with discretionary ligatures doesn't the "Special Ligatures" option appear in the Typography panel? I can't seem to access those ligatures.
(Zapfino is a .ttf, my font an .otf, if that matters.)