Why, you may ask, would you ever want to do this? Only you can answer that question, of course, but the QuickTime Player does have one really interesting attribute as a text player–it converts all the fonts into vector graphics, so the text will scale up beautifully as you resize the QuickTime Player window–no jaggies anywhere to be found.
Open any text file in QuickTime Player, then choose File -> Export. Set the Export pop-up menu to “Text to Text,” give your new file a name and save location, then click Save. Open the exported file in any pure text editor, and you’ll see how QuickTime formats your text for display in the QuickTime Player:
You can edit this file as you wish, but you’re not restricted to what you see there. A full set of text descriptors lets you change the font face and style, alignment, color, and a slew of other parameters. If I go any deeper than this, though, I’ll really be in over my head, as this is far from my area of expertise. Suffice it to say that if you’re interested in text tracks in QuickTime, it’s pretty easy to start playing around with them.