Feature request: proc_macro with content as string

I wonder if Rust could eventually allow something like #[proc_macro_string] or #[proc_macro_block]. White space, en dash and other things makes things harder than needed when implementing a macro, at the moment. The idea is to take take the block as string and pass it to the macro.

Example:

#[proc_macro_block]

pub fn html(input: &str) -> TokenStream {

// process input block

}

Usage:

let content = html! {

<h1>The string to process</h1>

};

I can work on this. Would the change be accepted?