Why doesn't the contents of a variable pass through a filter in Jade?

Question

Pug

Here is my template:

block content
  h1= title
  :markdown-it #{message}

I tried different options:

:markdown-it= message
:markdown-it!= message
:markdown-it message

:markdown-it
  #{message}

As a result, the content of `message` falls out in the same form, without filtering.
At the time, the following code works:

:markdown-it
  # Markdown
  I often like including markdown documents.