Example of jade blocks not rendering properly in Locomotive

mainview.jade

doctype 5
html(lang="en")
  head
  body
    .container
      // subview.jade content should appear here, but doesn't
      block content

route.js

app.get('/', function(req, res){
  res.render("subview");
});

subview.jade

extends mainview

block content
  .hero-unit
    h1 Hello, world.