+ /// Map a token down from macro input into the macro expansion.
+ ///
+ /// The inner workings of this function differ slightly depending on the type of macro we are dealing with:
+ /// - declarative:
+ /// For declarative macros, we need to accommodate for the macro definition site(which acts as a second unchanging input)
+ /// , as tokens can mapped in and out of it.
+ /// To do this we shift all ids in the expansion by the maximum id of the definition site giving us an easy
+ /// way to map all the tokens.
+ /// - attribute:
+ /// Attributes have two different inputs, the input tokentree in the attribute node and the item
+ /// the attribute is annotating. Similarly as for declarative macros we need to do a shift here
+ /// as well. Currently this is done by shifting the attribute input by the maximum id of the item.
+ /// - function-like and derives:
+ /// Both of these only have one simple call site input so no special handling is required here.