Function start 

pub fn start<S>(name: S) -> Start<S>
where
    S: AsRef<str>,

Available on crate features html and http only.

Emit a <?start name="…"> processing instruction — the opening of the range form of declarative partial updates. Whatever HTML sits between <?start name="x"> and the matching end (often a skeleton or spinner) is replaced wholesale when the <template for="x"> arrives, so the placeholder content goes away on swap without any CSS bookkeeping. The name is HTML-escaped via escape_into on render.