Paragraphs can be numbered, but not lines, since the size of the text can be changed.
There is really no consensus yet about the ideal way to handle references, nor the ideal reader either, since displaying formulae, etc is not something many readers do well. If they all share the same device, or something like that...
But my device does not connect to the internet, so a link is worthless to me, so referencing that way doesn't help me.
Welcome to the Wild West.