Is there a way to further search within search results? This is when you want to further delimit and narrow down your search.
Yes. First make sure, that you show your results in a collection (search window -> upper right side -> "result in". This will find the first matches.
Then you can search inside that collection by typing searchitems (replace this with whatever you want to filter, "*" are also both to be typed). For this you have to activate in the preferences -> lister -> file view -> "use search field" (please note that the english translations might be somewhat different, i am looking at a german version.
Anyway, this enables you to make multiple searches. when you purge your results (results will accumulate otherwise), use "remove from collection button" only, so you will not have you original files deleted.
Searching inside collections didn't work too well the last time I tried it. It's best to create a search/filter and then modify the search/filter and search again if you want more restricted results. (The second search is usually very fast since Windows caches most of the data, unless you're doing a contents search of a large amount of data.)