Option + delete behaviour

Deleting the previous word (`option + delete`) in MacDown seems to ignore formatting, which is unexpected and different from other tools I'm used to writing in (e.g. Sublime, Word).

E.g. If I have written the following document, and I'd like to remove the subtitle. (`|` denotes my cursor)

``` md
# My Title
## Subtitle|
```

I press `option + delete` once:

``` md
# My Title
## |
```

Then again:

``` md
# My |
```

Now half my title is gone.
##

Whereas in Sublime:

``` md
# My Title
## Subtitle|
```

``` md
# My Title
## |
```

``` md
# My Title
|
```

Is this desirable?

No source file or test is identified. Reproduce the reported Option+Delete sequence in MacDown with the Markdown heading example, then trace the editor's word-deletion behavior; it is done when deletion removes the subtitle text without consuming the preceding heading or title text.

Written by the indexing model from the issue text.