An earlier question on JP.SE asked about the usage of the particle「に」for what seemed to be attribution or possession, but I wasn't sure if those were 'official' uses of「に」and I decided to do some digging. I found an explanation on the sentence structure NにNがあります／います where「に」links back to a location where something or someone exists. Scrolling down for alternative uses, I found the following explanation for「Nがあります／Nがいます」in particular:
I interpreted this as "Using「Nがあります」or「Nがいます」indicates a notion of possession." However, I'm not quite sure as to what「余裕があれば」means in this context. Maybe something like for those who want to learn more or something?
If this is indeed the right interpretation, are these cases inherently implied to follow the「NにNがあります／います」pattern, i.e. is it just a fixed pattern such as 「～は～が～」or is there a more explicit motivation for the usage of「に」in this sense? Or, alternatively, is it unrelated to the initial「に」but more of a use case particular to「が」(this seems unlikely)?