KinoSearch::Document::Doc is a Doc object that is akin to a row in a database, in that it is made up of several fields, each of which has a value. Doc objects are only created via factory methods of other classes.
my $doc = $invindexer->new_doc;
$doc->set_value( title => $title );
$doc->set_value( bodytext => $bodytext );
$doc->set_value( title => $title_text );
my $text = $doc->get_value( 'title' );
set_value and get_value are used to modify and access the values of the fields within a Doc object.
boost is a scoring multiplier. Setting boost to something other than 1 causes a document to score better or worse against a given query relative to other documents.