If you are using an execution context that inherits from the NameRecorderMixin (nearly all do -- see chapter 8) then the execution context will raise a ApplicationError exception if multiple instances of some types of input tag with the same name are added to a form. The list attribute of the <al-input> tag is used indicate that multiple instances are intentional.
The presence of the list attribute on an <al-input> tag makes the request merging in the NameRecorderMixin class place any browser request values for the field into a list (field not present is represented by the empty list).
The attribute must not be used for input field types radio, submit, and image. The attribute is ignored for the file input field type.