If you are an organized sort of person who likes to remember what the hell you were trying to do when you ran a particular simulation you might find it useful to put comments in your input file. In PLUMED you can do this as comments can be added using a # sign. On any given line everything after the # sign is ignored so erm... yes add lines of comments or trailing comments to your hearts content as shown below (using Shakespeare is optional):

Click on the labels of the actions for more information on what each action computes
# This is the distance between two atoms:
d1: DISTANCE ATOMSthe pair of atom that we are calculating the distance between. =1,2
Snout: UPPER_WALLS ARGthe input for this action is the scalar output from one or more other actions. =d1 ATcompulsory keyword
the positions of the wall. =3.0 KAPPAcompulsory keyword
the force constant for the wall. =3.0 # In this same interlude it doth befall.
# That I, one Snout by name, present a wall.


(see DISTANCE and UPPER_WALLS)

An alternative to including comments in this way is to use the command ENDPLUMED. Everything in the PLUMED input after this keyword will be ignored.