Boxes with autocompletion

Question

Entities have this nice autocompletion of properties:

How do I define autocompletion for my own boxes that behave the same way?

Answer 1

Here is a simple example to implement custom do...end box:

ClearAll@do
SetAttributes[do, HoldAll];
do[var_, begin_, end_, body_] := Do[body, {var, begin, end}]
Hold[do /: MakeBoxes[do[var_, begin_, end_, body_], StandardForm] := 
     TemplateBox[MakeBoxes /@ Unevaluated@{var, begin, end, body}, 
      "do", DisplayFunction -> (GridBox[{{RowBox@{RowBox[{style@"do", 
                " ", #}], "=", 
              RowBox[{#2, " ", style@"to", 
                " ", #3}]}}, {RowBox@{"", #4}}, {style@"end"}}, 
          ColumnAlignments -> Left] &)]] /. 
   style[str_] -> StyleBox[str, FontColor -> Darker@Green] // 
  ReleaseHold // ReleaseHold
Hold[CurrentValue[EvaluationNotebook[], {InputAliases, "do"}] = 
    TemplateBox[{"[SelectionPlaceholder]", "[Placeholder]", 
      "[Placeholder]", "[Placeholder]"}, "do", 
     DisplayFunction -> (GridBox[{{RowBox@{RowBox[{style@"do", 
               " ", #}], "=", 
             RowBox[{#2, " ", style@"to", 
               " ", #3}]}}, {RowBox@{"", #4}}, {style@"end"}}, 
         ColumnAlignments -> Left] &)]] /. 
  style[str_] -> 
   StyleBox[str, FontColor -> Darker@Green] // ReleaseHold

When using, first press Esc key, then input do, then press Esc key to automatically incomplete.