Sometimes it is handy to put comments in the algortihm section to explain and later remember how the algorithm works. You can enter comments by starting a line with a ':' and ending it with a ';' like:
:# You can enter comments by starting with a colon ':' and ending the line with a semicolon ;
I usually add a '#' directly after the ':' to make it more visible. It is not necessary.
NB: Apparently using a single quote ' within your comment line, like using the word don't in your commentline can cause malfunction. Better write
":# do not #;
in stead of
":# don't #;