I think you're missing the point Leon is trying to make.  He's saying that,
in ES 6 we have a new way to write strings.  In some ways, these more
powerful strings may condition some people to use ` as their main string
delimiter.  An unsuspecting person may liken this to PHP's double quotes vs
single quotes, thinking that the only difference is that you can use
`${variable}` in strings that are delimited with backticks, but other than
that everything is the same.  When they write this in their code:

```
`use strict`;
```

They may introduce bugs by writing non-strict code that doesn't throw when
it should.  Adding it to the spec wouldn't be difficult and it would avoid
any potential confusion or difficult-to-debug issues.  It's definitely
easier than educating people, IMO.

On Thu, Feb 5, 2015 at 10:56 AM, Mathias Bynens <mathias at qiwi.be> wrote:

>
> > On 5 Feb 2015, at 11:04, Leon Arnott <leonarnott at gmail.com> wrote:
> >
> > Well, that isn't quite the full story - if it were just a case of
> pragmas having to use something, anything, that could pass ES3 engines,
> then there wouldn't necessarily be two otherwise-redundant forms of the
> syntax - `"use strict"` and `'use strict'`. The reason those exist is to
> save the author remembering which string delimiter to use - it mirrors the
> string literal syntax exactly.
>
> If that were the case, then e.g.
> `'\x75\x73\x65\x20\x73\x74\x72\x69\x63\x74'` would trigger strict mode. (It
> doesn’t, and that’s a good thing.)
> _______________________________________________
> es-discuss mailing list
> es-discuss at mozilla.org
> https://mail.mozilla.org/listinfo/es-discuss
>
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I think you're missing the point Leon is trying to make.  He's saying that,
in ES 6 we have a new way to write strings.  In some ways, these more
powerful strings may condition some people to use `` ` `` as their main string
delimiter.  An unsuspecting person may liken this to PHP's double quotes vs
single quotes, thinking that the only difference is that you can use
`` `${variable}` `` in strings that are delimited with backticks, but other than
that everything is the same.  When they write this in their code:

```
`use strict`;
```

They may introduce bugs by writing non-strict code that doesn't throw when
it should.  Adding it to the spec wouldn't be difficult and it would avoid
any potential confusion or difficult-to-debug issues.  It's definitely
easier than educating people, IMO.