> This is probably to support potential ambiguities and intraword emphasis e.g. underscore is a common pseudo-space so doesn't support intraword use but * does e.g.

    is_not_italic

    this*is*italic.

That seems like a legacy spec mistake they had to adhere to. I'd expect

    this_is_italic

to work and for _ literal usage to require

    is\_not\_italic