Highlighter Pens
A highlighter pen is a fluorescent ink felt pen that is used to draw and mark important areas. The twin type, which has pen tips of different thicknesses on each side of the pen shaft, is commonplace, and allows differentiation by the side of characters drawn. The cap on the thicker side has a hook to help you secure it to your breast pocket, etc. Normally, the pen tip is covered with a cap, but with a knock type there are cases where the pen tip can be taken in and out. There is a wide variety of ink colors, and there are cartridges that support refilling and ink that refills a pen that is inserted into it. Most highlighter pens cannot be erased once they are drawn, but there are also types which allow mistakes or overdrawn lines to be easily erased by rubbing them out.