Try selecting any portion of this paragraph. A toolbar should appear right above the beginning of your selection, offering ways to act on the highlighted text. The selection itself is just a regular browser selection, so it keeps every native affordance you already know.
Drag across multiple paragraphs, reverse direction, or use a keyboard shift-select. The toolbar tracks the start of the selection and repositions when the page scrolls. On touch devices it appears after you finish dragging the selection handles.
Tapping a toolbar action receives the selected text and dismisses the toolbar by default. The actions themselves are unopinionated, so the component can host quote and share, code highlights, citation footnotes, or anything else worth doing with a slice of prose.