From https://drafts.csswg.org/css-lists/#list-style-position-property
inside
No special effect.
outside
[...] the marker box [...] be placed on the inline-start side of the box, using the writing mode of the box indicated by marker-side.
Does this mean that marker-side only affects outside markers?
But https://drafts.csswg.org/css-lists/#marker-side talks about markers in general.
It's not clear how inside markers would be affected, though.