Exporter default_config merging

[tuncbkose]

In exporters templateexporter, html, latex, markdown,rst and asciidoc, the following is present

@property
def default_config(self):
    c = Config( some stuff here )
    c.merge(super().default_config)
    return c

where in the merging, the configuration of the exporter can be overwritten by the parent configuration. In other words, if self and super() contain different values for the same setting, the resulting config will contain the super()s setting.

I am a bit confused about why this is the case. My expectation is that the reverse should take place: a subclass should inherit its parent's configuration and modify it according to its own needs.

As a quick check, I replaced the line that is merging with

if super().default_config:
    c2 = super().default_config.copy()
    c2.merge(c)
    c = c2

and the tests are still passing (except for some skipped ones due to not installed programs).

Is there a reason why the former is preferable to the latter style of merging configs?