I’ve found first answer in this topic on StackExchange extremely representative.
That reminded me discussion we had when were designing the first version of Evernote application.
Challenge there was to provide UI that allows the user to find notes quickly without need of excessive scrolling.
Each note may have so called tags (a.k.a. labels) assigned. By clicking on tag (left side bar) the tape will get filter applied – only notes with such tag are shown.
By expanding the tag (“+” sign) you can see intersection of notes that have this tags and some others. For example here click on hello->world (on the left) will give you set of notes with the condition
has-tag:"hello" AND has-tag:"world" (see top bar):
And if you type “wonderful” in the search field you will get filter
has-tag:"hello" AND has-tag:"world" AND has-text:"wonderful" applied.
Pretty convenient I would say.