The Manuscripts editor includes so-called "gutter helpers", designated with the blue + and o symbols in the left margin for the currently active paragraph. These symbols are buttons that lead you to shortcut actions for inserting (the + symbols) and manipulating (the o) the document contents in a way that is contextual.
The gutter insertion helper (+ symbol)
The gutter selection helper (o symbol)
The following example shows what the gutter selection helper tool presents in the case of a paragraph.
The gutter helper is however entirely optional and can be toggled on or off from the Editing Preferences by choosing "Show smart gutter in the left margin when editing".