Optinal variables enclosed in square brackets. For example Array.join([separator])
In function description variables are bolded. For example Math.sqrt(num) - square root ofnum
Undefined number of arguments in function written as name... and function description name are all these variables in general, and name[n] either name. For example Array.concat(elements...) - returns array that containg elements fromArray andelements ifelements[n] is array then to the array that returns are added all elements fromelements[n].