It seems in our project using Middleman, Sevilta does not support extensions using html.md although saving and defining these in our config.yml file:

collections:
  - name: "case_studies"
    label: "Case studies"
    format: "yaml-frontmatter"
    extension: "html.md"
    folder: "source/case_studies/en"
    create: true
    identifier_field: title
    fields:
      - {label: "Title", name: "title", widget: "string", required: true}

While changing this to a supported extension, like md the browser produces markup html and doesn't render the page correctly.

Is there a way this can be supported?