The site discusses Dirac delta function for solving point energy source localized in spacetime. However, personally, I have a lingering suspicion that at the fundamental infinitesimal region of spacetime, there are two energy sources: one with the immeasurable value of zero and the other with the immeasurable value of infinity. When these two sources are in dynamic equilibrium then EM field are created.
http://www.sci.hkbu.edu.hk/msc/full/billy/node5.html
The speed of transformation between these two energy sources is measured as the speed of light of Maxwell's classical electromagnetism.