With regards to this function
// Returns a list of letters
// letterType {string} - “All”, “Consonants”, or “Vowels”
// upper {boolean} - whether the letters should be upper case. If false, returns lowercase
// return {list} - a list of letters
function getLetters(letterType, upper)
I do not understand how the computer knows that the “upper” parameter is a boolean argument.
Thanks in advance for help.