Text::Annotate::DataSource - parent class for annotation data sources
An annotation datasource provides two things: a) a way to look up potential key phrases. Key phrases that match our data yield URIs or similar identifiers. b) a way to "explain" those URIs, producing a brief HTML description of the phrase in question.
$datasource->index_lookup ("get", "your", "widgets", ... "getyourwidgetsfrom", "wigentiacorp")
index_lookup is called with a list of (already canonicalised) key phrases. Where those phrases match one we know about, we return a two-element list.
It is passed a list so we don't get overwhelmed by function-switching overhead, whilst painstakingly trundling through piles of useless words in search of something interesting.
You may well want to override this.