Tooltips

Code	Place the mouse cursor over an identifier in the editor. A tooltip shows the full signature of the element under cursor and the comment associated with the element’s declaration (written above or the side).
Folded regions	Place the mouse cursor over the + sign of a folded code region. A tooltip shows the folded region contents.
Problems	Place the mouse cursor over an error or warning annotation on the left vertical ruler of the editor. A tooltip shows the error or warning message. If you hover the squiggled identifier you will also see a tooltip including quick fix proposals.