Filtering feeds by tag content other than <title>?

[silaxe]

Hello,
I'm very new to the RSS world and not at all a developer. I would like to use a 'keep rule' to filter specific content of the tag of this rss feed: https://www.consilium.europa.eu/en/register/rss/thmenv.xml/.
I'm a bit confused whether this is now possible or whether it is still only possible to filter content of the <title> tag of a rss feed.
If this is possible, how should it be written in the keep rule?
Thanks in advance for your help!
Silaxe