Invalid nested HTML comments in generated MSO conditionals

[clj]

I just updated mjml-python from 1.2.3 to 1.3.0, (which as far as I can gather changes the linked MRML from version 2.0.0-rc3 to 3.0.0). This caused our do our emails parse as HTML canary to trip up on output generated from MJML code like this:

<mjml>
    <mj-body>
        <mj-section>
        <!-- A comment -->
        </mj-section>
    </mj-body>
</mjml>

I have cut the generated code to only show the relevant bits, but added newlines and indentation to the MRML generated code.

mjml-python 1.3.0 (mrml 3.0.0)

<td style="direction:ltr;font-size:0px;padding:20px 0;text-align:center;">
  <!--[if mso | IE]><table border="0" cellpadding="0" cellspacing="0" role="presentation"><tr><!-- A comment --></tr></table><![endif]-->
</td>

mjml-python 1.2.3 (mrml 2.0.0-rc3)

<td style="direction:ltr;font-size:0px;padding:20px 0;text-align:center;">
  <!--[if mso | IE]><table border="0" cellpadding="0" cellspacing="0" role="presentation"><![endif]--><!--[if mso | IE]><tr><![endif]-->
  <!-- A comment -->
  <!--[if mso | IE]></tr><![endif]--><!--[if mso | IE]></table><![endif]-->
</td>

mjml.io

<td style="direction:ltr;font-size:0px;padding:20px 0;text-align:center;">
  <!--[if mso | IE]><table role="presentation" border="0" cellpadding="0" cellspacing="0"><tr><![endif]-->
  <!-- A comment -->
  <!--[if mso | IE]></tr></table><![endif]-->
</td>

It looks like mjml.io's implementation detects the comment and ends the MSO conditional, and that MRML prior to version 2.0.0 had the same behaviour. I'm not sure if the behaviour change in later versions is intentional, or if a dependency caused this change. However, the new behaviour might be surprising to users since it is different from that of the reference MJML implementation (and generates a nested comment, i.e. invalid HTML).

Personally I am considering stripping HTML comments before passing the template to MRML anyway.

Thanks for a great library though!

[jdrouet]

thanks for this! I'll take a look 😜