[Grammar] Comma Question

[EmaNekaf]

I keep encountering instances where I use things like this, and I'm unsure as to the proper way of punctuating them. I don't know the technical term for it, but what is the proper way to punctuate sentences that have an insert-the-technical-name-for-the-element-here (whatever the "in some cases" is acting as in the following two sentences)?
a. I found that all the hardships were necessary to the plot, character development, or, in some cases, both.
b. I found that all the hardships were necessary to the plot, character development, or in some cases, both.
Or am I just off altogether, and neither is correct? In which case, please enlighten me. If you could tell me the name of said sentence element, that would also be great.
Thanks!

 

[emsr2d2]

At the end of both of Robert's sentences, I would punctuate like this:

... character development or, in some cases, both.

"in some cases" is the additional information. Without the commas and the additional information you would be left with "or both" which is correct.