Is not true the important is got the hole idea Js

See you are there in the MDN and see something like that  

const musicTypes = document.selectForm.musicTypes;

And nobody explains what that means...

And means that look for the part of the document so we are talking about HTML, I said before that the importance of the DOM is write JS no matter that DOM is something that is in the HTML, so that is a sequence of nodes from the HTML, so to I find the element that I want to access in the Script in the HTML or document, I am describing the nodes, so the more older parent is the 'document' (all is about document, very impressive) and the 'document' is parent of the 'selectForm', in other words, the 'selectForm' is a son of the 'document', and 'musicType' is a son of 'selectForm', in the HTML of the code, we have a tag that the id is 'selectForm' and inside the 'selectForm' we have a tag that the id is 'musicTypes'.

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