I'm trying to learn about SpannableStrings, and it is boiling down to this
setSpan method:

http://developer.android.com/reference/android/text/SpannableString.h...,
int, int, int)

However, of course, the method is completely undocumented, and it is not
clear what ought to be passed into the first
parameter.  Am I missing something here, or did they just forget to write
this?

As far as I understand the first argument: it is whatever object you want
to use for tagging that span of text. It's up to your app to come up with
the right interpretation. If you want to use the span for formatting you
can use one of the CharacterStyle<http://developer.android.com/reference/android/text/style/CharacterSt...>objects as first argument.

Here is a tutorial about rich style formatting with spannable strings:
http://www.chrisumbel.com/article/android_textview_rich_text_spannabl...