asp.net mvc - Why is my display template not applying classes? -

i have displaytemplates string , datetime?, these:

@model string @html.textboxfor(m => model, new { @class="read-only"})  @model datetime? @{     string modelvalue = "";     if (model.hasvalue)     {         if (model.value != datetime.minvalue)         {             modelvalue = model.value.toshortdatestring();         }     } } @html.textbox("", modelvalue, new { @class = "date-picker date-text read-only", @readonly="readonly" }) 

i because when use helper displayfor prefer textbox darker background, , tag on date-picker class later transform these fields proper date pickers.

the class read-only defines background colour. in excerpt model,

[editable(false)] [display(name = "file name")] public string filename { get; set; }  [editable(false)] [display(name = "file report date")] public datetime? filereportdate { get; set; } 

two properties identical, yet display template string refuses add read-only class, template datetime right.

why there such difference, , why won't display template add class inner input element?

added: seems template string not being used @ all. why be?