Source Code is instructive code for a computer written out in “long form.” That is to say, no compiler has done any work to perhaps optimize the code for execution in the actual operating environment. This differentiation from code that you write, at first, will not be extremely important. What you should know now is that the dojo is actively parsed as you enter in code. This prevents you from entering code that is syntactically invalid (you can still make logical mistakes, or type mistakes).