{{/* Input: dict {"responsive": [RESOURCE, ...], "imageBasePath": "/images/lazyimg"} */}}
{{ $images := .responsive }}
{{ $base := default "/images/lazyimg" .imageBasePath }}
{{ $srcset := slice }}
{{ range $images }}
  {{ $u := path.Join $base (strings.TrimPrefix "/" .RelPermalink) }}
  {{ $srcset = append (printf "%s %dw" $u .Width) $srcset }}
{{ end }}
{{ return (delimit $srcset ",\n") }}