Talk:Line element/to do

Tasks for expert:
 * completely rewrite, bearing in mind applications in physics
 * better discussion of 2,3,4+ dimensions, e.g. properties of metric tensor special to low dimensions
 * clarify Riemannian versus semi-Riemannian manifolds
 * clarify flat versus nonflat spaces, spacetimes
 * better examples (give range of coordinates, specify whether any functions used are arbitrary smooth or whatever)

Tasks for anyone:
 * improve diction