The date the feed was last modified, as a string in the same format as it was published in the original feed.
This element is parsed as a date and stored in feed.modified_parsed.
Comes from
- /atom:feed/atom:modified
- /rss/channel/pubDate
- /rss/channel/dc:date
- /rdf:RDF/rdf:channel/dc:date
- /rdf:RDF/rdf:channel/dcterms:modified