The search works with direct and indirect matches for both artist or songs. All direct matches are bolded, and the indirect matches aren't, but they are still visible.
If you type the name of a song and it could be searched this song will be considered a direct match. It will be bolded, and the artist for this song will be displayed as an indirect match. All the other songs by the same artist and all the other artists and songs will be hidden.
If you type the name of an artist/band and it was found, this band will be considered the direct match. So, every song of them will be considered indirect matches and be displayed. All other artists and songs by different artists will be hidden.
The counter shown below the search box consider every match, both direct or indirect.