“patterns” is just not well documented. functionCall in particular is newer. Here’s what I notice…
p.functionCall.parse(this.latex).term1.identifier outputs function name latex.
p.functionCall.parse(this.latex).term1.n outputs the number of parameters.
p.functionCall.parse(this.latex).term1.nth(2) outputs the latex of a parameter (the second in this example).
There’s also this thread talking about how it doesn’t play well with p.product.