There's a lot of info online on how the long s (ſ) was used in past spelling, but not a lot about why it appears in the alternate forms it does, and what the expectations are today in modern type design if and when (rarely ever) its included or used.
I've linked a few samples below, including ligatures ( long s+small roman s, which is often mistaken for the Esszett) for reference (nb. the normal ff ligature is included in comparison to the ſſ ligature).
The alternation between Regular & Italic is of course the descender, which follows the same change as the lowercase 'f' between Regular & Italic.
The inconsistent aspect which I'm highly curious about, and for which no apparent explanation is available to me, is the left-hand bar which appears on some typefaces, and not on others, or features only in either the Italic or Regular of the given type.
What are your thoughts on these reasons? And on good design for the long s?