Listing 15. You can use regular expressions as filters.

PREFIX dc:   <http://purl.org/dc/elements/1.1/>
PREFIX xsd:  <http://www.w3.org/2001/XMLSchema#>
PREFIX rss:  <http://purl.org/rss/1.0/>
PREFIX content: <http://purl.org/rss/1.0/modules/content/>

DESCRIBE ?channel ?bnode ?a WHERE
{
 ?channel ?items ?bnode .
 ?bnode ?hasitem ?a .
 ?a content:encoded ?content .
 FILTER ( regex(?content, ".*product.*", "i") )
}