This excerpt from a user manual for a video-game player that displays 3D images describes two of the safety risks associated with playing video games.

Notice that the excerpt uses mandatory language: “You must . . . .” Although politeness is desirable most of the time, you don’t want to sound as if you were making suggestions or asking readers to do you favors. For instance, if a task calls for using safety goggles, do not write “You should consider wearing safety goggles.” Instead, write “You must wear safety goggles when operating this equipment.”

This set of safety information defines the keywords warning, caution, and important.

The safety information goes on to discuss eyestrain and motion sickness, repetitive motion injuries, and radio frequency interference.