I'm currently reading Schwartz's book and at page 489 he defines the Wilson Line field and writes in closed-form given by $$ W_P(x,y)=\exp\left(ie \int\limits^x_y A_\mu(z) dz^\mu\right) $$
I'm looking for some reference that describes it (and related things like Wilson Loops) in a principal bundle language, with more details than the wikipedia article provides.
I'd appreciate any suggestion.
I think the book "Differential Geometry and Mathematical Physics: Part II. Fibre Bundles, Topology and Gauge Fields" is a very clear reference for these topics.