Multiline non-compiled attribute in jade

I tried to do so:

body(
  |{% case page.url %}
  | {% when '/' %}
  |    class="hellopage"
  | {% when page.url contains '/gallery/' %}
  |    class="gallerypage"
  |{% endcase %}
  )

This {% .. %} stuff for Liquid actually.
So, it is not compiled. How can I write a multi-line attribute in tag?

EDIT:

The problem is that the Pug compiler does not like the {% character sequences in the attribute. In your specific scenario, this the work-around would be to escape the newlines and put Liquid logic in the attribute value string, as well:

body(class="\
   {% case page.url %}\
    {% when '/' %}\
       hellopage\
    {% when page.url contains '/gallery/' %}\
       gallerypage\
   {% endcase %}"
  )

Old answer:

I don't think that you need the pipe character (|) to do this. Attributes on multiple lines are supported by Pug. Something like this should be sufficient:

body(
   {% case page.url %}
    {% when '/' %}
       class="hellopage"
    {% when page.url contains '/gallery/' %}
       class="gallerypage"
   {% endcase %}
  )

Should work, but haven't tested it though (due to a lack of a Liquid+Pug testing environment).