Mixed fraction input

You can add an input alias to do this. For example:

CurrentValue[EvaluationNotebook[], {InputAliases, "mf"}] = TemplateBox[
    {"\[SelectionPlaceholder]","\[Placeholder]","\[Placeholder]"},
    "MixedFraction",
    DisplayFunction->(RowBox[{#1, FractionBox[#2,#3]}]&),
    InterpretationFunction->(RowBox[{#1,"+", FractionBox[#2,#3]}]&)
];

Here is a short animation showing it in action:

\[ImplicitPlus] can be entered as ESC+ESC:

5\[ImplicitPlus](1/2)
(*  11/2  *)

It works for entering in the Front End, but it is automatically converted to Plus: