Comments that look like: (debug, rest of comment) are the same as comments like (msg, rest of comment) with the addition of special handling for parameters (below).
Comments that look like: (print, rest of comment) are output to stderr with special handling for parameters.
For example: to print a named global variable to stderr (the default console window) add a line to your gcode like...
(print,endmill dia = #<_endmill_dia>)
Inside the above types of comments, sequences like #123 are replaced by the value of the parameter 123. Sequences like #<named parameter> are replaced by the value of the named parameter. Remember that named parameters will have whitespace removed from them. So, #<named parameter> is the same as #<namedparameter>.