XF 2.1 How does Xenforo RSS Feed importer determine new entries?

[Techie43]

Hello,

I am importing threads into Xenforo from a MySQL database using an RSS feed.

Basically, I insert the RSS feed URL into the Xenforo RSS importer and it creates threads from the database rows.

I am also using RSS Feed Filter add-on to limit the number of entries in a single RSS import.

I wanted to know that how does Xenforo RSS Feed importer determine "new" entries.