XOHM supports the use of Boolean Searches in the form of "AND", "OR" and "NOT". To search for documents with cats and dogs just type "cats AND dogs" not including the double quote marks. Of course, this is also the default query and is equivalent to a search for "cats dogs". To search for articles with cats or dogs, but not both, use "cats OR dogs". To search for articles with cats but not dogs enter "cats NOT dogs". To search for a specific sequence of words you may surround your query by the double quotation marks: "cats and dogs" including quotes.
Most people just look at the top ten results. If you want more in your aggregated list, increase this number. The more you select, the longer it takes to get them, so if you select the maximum of 100 results, it will take a few seconds.