Where is this ASP.NET feature documented? <%= string format, params object[] args %>

Question

Apparently it is possible to write formatted output using the <%= %> construct (render block) in ASP.NET web forms pages and views.

<%= "{0} is {1}", "Foo", 42 %>

This will render "Foo is 42". As far as I know the ASP.NET parser translates <%= %> into a call to HttpResponse.Write(string). Obviously in the code above, there is no one-to-one translation, because the number of arguments don't match (assuming the , in the expression above separates arguments).

Now I have seen that the class TextWriter has a Write(string, object[]) method.

I have checked the output from the parser, and indeed it calls the TextWriter's method that accepts a params object[] argument for formatting:

private void @__Renderform1(System.Web.UI.HtmlTextWriter @__w, System.Web.UI.Control parameterContainer) {
    // ...
    @__w.Write( "{0} is {1}", "Foo", 42 );

Is that behavior documented anywhere?

Answer 1

As far as I know the ASP.NET parser translates <%= %> into a call to HttpResponse.Write(string).

Maybe the <%= "{0} is {1}", "Foo", 42 %> is translated to Response.Output.Write(string format, params object[] arg), Output being of type TextWriter, which would be the explanation according to http://www.hanselman.com/blog/ASPNETResponseWriteAndResponseOutputWriteKnowTheDifference.aspx