What is the difference between epub and ios.epub formats?

Question

iOS

The Litres website sells e-books and the epub format is presented there in two forms: epub and ios.epub They have a vague description
on the website:
.epub is an HTML-based format actively promoted by Adobe. Supported in almost all modern programs and devices;
.ios.epub - ePub documents adapted for viewing on iOS devices;
I tried to find details of what is the more detailed difference and what kind of adaptation for iOS, but to no avail. Technical support of Litres does not give an answer (maybe he waited a little).
Does anyone know what's the difference?

Answer 1

I won’t say exactly how it was with Litres, but in another publishing house where I worked, this meant that the epub was checked in iBooks and opens correctly there, all sections are visible and nothing moves out anywhere.