code: func (r *Registry) ColNumber(templateName string, node ast.Node) int {
  	var src, ok = r.sourceByTemplateName[templateName]
  	if !ok {
  		log.Println("template not found:", templateName)
  		return 0
  	}
  	return 1 + int(node.Position()) - strings.LastIndex(src[:node.Position()], "\n")
  }
docs: // ColNumber computes the column number in the relevant line of input source for the given node
  // within the given template.