I'm trying to load the rss content provided by Yahoo Finance, for example, from http://finance.yahoo.com/rss/headline?s=yhoo (which actually seems to redirect toward (http://feeds.finance.yahoo.com/rss/2.0/headline?s=yhoo®ion=US&lang=en-US).
Anyway, the point is the url will only provide 20 <item> and I'd like to load more than that. Feedly doesn't seem to have any problem doing so, so maybe there's a query parameter I'm not aware of?
Services like Feedly store feed history, but feed publishers usually don't provide older feed entries. So your best bet is to use Feedly's api: https://developer.feedly.com/v3/streams/
See also: How to get more feeds from RSS url?