What, exactly, is a FastTag Component?

[PaulMansour]

Apologies in advance if this is a silly question (I'm not a python programmer).

I think I have read most of the documentation on FTs, and it appears the result of Div, H1, Head etc., is a three-item tuple (the tag, the content, and the attributes). That is, an FT is not a class or object that supports public properties and methods in order to manipulate it. Is this a correct understanding?

I'm trying to understand how one might, say, extract or modify the content or attributes of an FT. For example, to the change content of an FT, does one just assign into the 2nd element the new content?
Can the tag itself be changed by just assigning a new value to 1st element?

Edit: I may be confusing things above by referring to the result of a FastTag as a FastTag. The docs say that a FastTag is a "callable", for example a function. What then does one call the result of the function? Is it also called a FastTag?