Add realt-time element highlighting like on https://www.websequencediagrams.com/ #124
Description
https://www.websequencediagrams.com/ reacts on your mouse coursor actions by higlightning parst of the image. We can do much better and more interactive, since we have SVG and control it. We just need to provide a way to have an association of the current node in AST (do we have AST?) with corresponding SVG node.
It also should work in other direction, when clicking or hovering diagram pieces it should highlight corresponding line of text in the editor.