### execution::start

A customisation point that notifies an operation state object to start its associated operation.

    constexpr unspecified start = unspecified;

The name `execution::start` denotes a customisation point object. The expression `execution::start(R)` for some subexpression `R` is expression-equivalent to:

- `R.start()`, if that expression is valid.
- Otherwise, `start(R)`, if that expression is valid, with overload resolution performed in a context that includes the declaration `void start();` and that does not include a declaration of `execution::start`.
- Otherwise, `execution::start(R)` is ill-formed.

##### Requirements

Header: `asio/execution/start.hpp`

Convenience header: `asio/execution.hpp`